1 files changed, 68 insertions, 0 deletions
diff --git a/qtjava/javalib/org/trinitydesktop/qt/WeakValueMap.java b/qtjava/javalib/org/trinitydesktop/qt/WeakValueMap.java
new file mode 100644
index 00000000..25989191
--- /dev/null
+++ b/qtjava/javalib/org/trinitydesktop/qt/WeakValueMap.java
@@ -0,0 +1,68 @@
+/** 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.trinitydesktop.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);
+		}
+	}
+}