ConcurrentHashSet.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 *
 */
package org.apache.mina.util;

import java.util.Collection;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * A {@link java.util.concurrent.ConcurrentHashMap}-backed {@link java.util.Set}.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class ConcurrentHashSet<E> extends MapBackedSet<E> {

    private static final long serialVersionUID = 8518578988740277828L;

    public ConcurrentHashSet() {
        super(new ConcurrentHashMap<E, Boolean>());
    }

    public ConcurrentHashSet(Collection<E> c) {
        super(new ConcurrentHashMap<E, Boolean>(), c);
    }

    @Override
    public boolean add(E o) {
        Boolean answer = ((ConcurrentMap<E, Boolean>) map).putIfAbsent(o, Boolean.TRUE);
        return answer == null;
    }
}