001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.mina.util;
021
022import java.util.Collection;
023import java.util.Set;
024import java.util.concurrent.ConcurrentHashMap;
025import java.util.concurrent.ConcurrentMap;
026
027/**
028 * A {@link ConcurrentHashMap}-backed {@link Set}.
029 *
030 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
031 */
032public class ConcurrentHashSet<E> extends MapBackedSet<E> {
033
034    private static final long serialVersionUID = 8518578988740277828L;
035
036    public ConcurrentHashSet() {
037        super(new ConcurrentHashMap<E, Boolean>());
038    }
039
040    public ConcurrentHashSet(Collection<E> c) {
041        super(new ConcurrentHashMap<E, Boolean>(), c);
042    }
043
044    @Override
045    public boolean add(E o) {
046        Boolean answer = ((ConcurrentMap<E, Boolean>) map).putIfAbsent(o, Boolean.TRUE);
047        return answer == null;
048    }
049}