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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.util;
21  
22  import java.util.Collection;
23  import java.util.Set;
24  import java.util.concurrent.ConcurrentHashMap;
25  import java.util.concurrent.ConcurrentMap;
26  
27  /**
28   * A {@link ConcurrentHashMap}-backed {@link Set}.
29   *
30   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
31   */
32  public class ConcurrentHashSet<E> extends MapBackedSet<E> {
33  
34      private static final long serialVersionUID = 8518578988740277828L;
35  
36      public ConcurrentHashSet() {
37          super(new ConcurrentHashMap<E, Boolean>());
38      }
39  
40      public ConcurrentHashSet(Collection<E> c) {
41          super(new ConcurrentHashMap<E, Boolean>(), c);
42      }
43  
44      @Override
45      public boolean add(E o) {
46          Boolean answer = ((ConcurrentMap<E, Boolean>) map).putIfAbsent(o, Boolean.TRUE);
47          return answer == null;
48      }
49  }