content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * Licensed 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.alibaba.nacos.common.utils;
  
  import java.util.AbstractSet;
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * Concurrent Hash Set implement by {@link ConcurrentHashMap}.
   *
   * @author <a href="mailto:liaochuntao@live.com">liaochuntao</a>
   */
  public class ConcurrentHashSet<E> extends AbstractSet<E> {
      
      private ConcurrentHashMap<E, Boolean> map;
      
      public ConcurrentHashSet() {
          super();
          map = new ConcurrentHashMap<>();
      }
      
      @Override
      public int size() {
          return map.size();
      }
      
      @Override
      public boolean contains(Object o) {
          return map.containsKey(o);
      }
      
      @Override
      public Iterator<E> iterator() {
          return map.keySet().iterator();
      }
      
      @Override
      public boolean add(E o) {
          return map.putIfAbsent(o, Boolean.TRUE) == null;
      }
      
      @Override
      public boolean remove(Object o) {
          return map.remove(o) != null;
      }
      
      @Override
      public void clear() {
          map.clear();
      }
  }
  