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Java > Open Source Codes > org > jruby > util > collections > WeakHashSet


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26 package org.jruby.util.collections;
27
28 import java.util.*;
29
30 /**
31  * A simple set that uses weak references to ensure that its elements can be garbage collected.
32  * See WeakHashMap.
33  *
34  * @author <a HREF="http://www.cs.auckland.ac.nz/~robert/">Robert Egglestone</a>
35  */
36 public class WeakHashSet extends AbstractSet {
37     private static final Object JavaDoc MAP_VALUE = new Object JavaDoc();
38     private WeakHashMap map;
39
40     public WeakHashSet() {
41         map = new WeakHashMap();
42     }
43
44     public boolean add(Object JavaDoc o) {
45         Object JavaDoc previousValue = map.put(o, MAP_VALUE);
46         return previousValue == null;
47     }
48
49     public Iterator iterator() {
50         return map.keySet().iterator();
51     }
52
53     public int size() {
54         return map.size();
55     }
56
57     public boolean isEmpty() {
58         return map.isEmpty();
59     }
60
61     public boolean contains(Object JavaDoc o) {
62         return map.containsKey(o);
63     }
64
65     public boolean remove(Object JavaDoc o) {
66         return map.remove(o) == MAP_VALUE;
67     }
68
69     public boolean removeAll(Collection collection) {
70         return map.keySet().removeAll(collection);
71     }
72
73     public boolean retainAll(Collection collection) {
74         return map.keySet().retainAll(collection);
75     }
76
77     public void clear() {
78         map.clear();
79     }
80
81 }
82
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