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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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.jboss.netty.util;
  
  import java.io.Serializable;
  import java.util.AbstractSet;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * A {@link Map}-backed {@link Set}.
   */
  final class MapBackedSet<E> extends AbstractSet<E> implements Serializable {
  
      private static final long serialVersionUID = -6761513279741915432L;
  
      private final Map<E, Boolean> map;
  
      /**
       * Creates a new instance which wraps the specified {@code map}.
       */
      MapBackedSet(Map<E, Boolean> map) {
          this.map = map;
      }
  
      @Override
      public int size() {
          return map.size();
      }
  
      @Override
      public boolean contains(Object o) {
          return map.containsKey(o);
      }
  
      @Override
      public boolean add(E o) {
          return map.put(o, Boolean.TRUE) == null;
      }
  
      @Override
      public boolean remove(Object o) {
          return map.remove(o) != null;
      }
  
      @Override
      public void clear() {
          map.clear();
      }
  
      @Override
      public Iterator<E> iterator() {
          return map.keySet().iterator();
      }
  }