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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.util;
17  
18  import java.io.Serializable;
19  import java.util.AbstractSet;
20  import java.util.Iterator;
21  import java.util.Map;
22  import java.util.Set;
23  
24  /**
25   * A {@link Map}-backed {@link Set}.
26   */
27  final class MapBackedSet<E> extends AbstractSet<E> implements Serializable {
28  
29      private static final long serialVersionUID = -6761513279741915432L;
30  
31      private final Map<E, Boolean> map;
32  
33      /**
34       * Creates a new instance which wraps the specified {@code map}.
35       */
36      MapBackedSet(Map<E, Boolean> map) {
37          this.map = map;
38      }
39  
40      @Override
41      public int size() {
42          return map.size();
43      }
44  
45      @Override
46      public boolean contains(Object o) {
47          return map.containsKey(o);
48      }
49  
50      @Override
51      public boolean add(E o) {
52          return map.put(o, Boolean.TRUE) == null;
53      }
54  
55      @Override
56      public boolean remove(Object o) {
57          return map.remove(o) != null;
58      }
59  
60      @Override
61      public void clear() {
62          map.clear();
63      }
64  
65      @Override
66      public Iterator<E> iterator() {
67          return map.keySet().iterator();
68      }
69  }