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