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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  }