content: /*
   * 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 com.alipay.remoting.util;
  
  import java.util.AbstractSet;
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  /**
   * Concurrent hash set.
   * 
   * @author yunliang.shi
   * @version $Id: ConcurrentHashSet.java, v 0.1 Mar 11, 2016 3:40:41 PM yunliang.shi Exp $
   */
  public class ConcurrentHashSet<E> extends AbstractSet<E> {
      private ConcurrentMap<E, Boolean> map;
  
      /**
       * constructor
       */
      public ConcurrentHashSet() {
          super();
          map = new ConcurrentHashMap<E, Boolean>();
      }
  
      /**
       * return the size of the map
       * @see java.util.AbstractCollection#size()
       */
      @Override
      public int size() {
          return map.size();
      }
  
      /**
       * 
       * @see java.util.AbstractCollection#contains(java.lang.Object)
       */
      @Override
      public boolean contains(Object o) {
          return map.containsKey(o);
      }
  
      /**
       * 
       * @see java.util.AbstractCollection#iterator()
       */
      @Override
      public Iterator<E> iterator() {
          return map.keySet().iterator();
      }
  
      /**
       * add an obj to set, if exist, return false, else return true
       * @see java.util.AbstractCollection#add(java.lang.Object)
       */
      @Override
      public boolean add(E o) {
          return map.putIfAbsent(o, Boolean.TRUE) == null;
      }
  
      /**
       * 
       * @see java.util.AbstractCollection#remove(java.lang.Object)
       */
      @Override
      public boolean remove(Object o) {
          return map.remove(o) != null;
      }
  
      /**
       * clear the set
       * @see java.util.AbstractCollection#clear()
       */
      @Override
      public void clear() {
          map.clear();
      }
  }
  