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/** From Section 12.5.3, Reference Queues page 324-326
of 'The Java Programming Language, Third Edition'.
But why wasn't it included in the java.util Collection package?
*/
package org.kde.qt;
import java.lang.ref.*;
import java.util.*;
public class WeakValueMap extends HashMap {
private ReferenceQueue reaped = new ReferenceQueue();
private static class ValueRef extends WeakReference {
private final Object key; // key for value
ValueRef(Object val, Object key, ReferenceQueue q) {
super(val, q);
this.key = key;
}
}
public Object put(Object key, Object value) {
reap();
ValueRef vr = new ValueRef(value, key, reaped);
return super.put(key, vr);
}
public Object get(Object key) {
reap();
ValueRef vr = (ValueRef) super.get(key);
if (vr == null) {
return null;
} else {
return vr.get();
}
}
/** Force an entry to be removed if it is known to be invalid,
rather than waiting for the garbage collector to put it
on the reaped queue.
*/
public Object remove(Object key) {
reap();
ValueRef vr = (ValueRef) super.get(key);
if (vr == null) {
return null;
} else {
vr.clear();
super.remove(key);
return null;
}
}
public int size() {
reap();
return super.size();
}
public void reap() {
ValueRef ref;
while ((ref = (ValueRef) reaped.poll()) != null) {
super.remove(ref.key);
}
}
}
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