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    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * License.  You may obtain a copy of the License at:
    7    *
    8    *    http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.util;
    17
    18  import java.io.Serializable;
    19  import java.util.AbstractSet;
    20  import java.util.Iterator;
    21  import java.util.Map;
    22  import java.util.Set;
    23
    24  /**
    25   * A {@link Map}-backed {@link Set}.
    26   *
    27   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    28   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    29   *
    30   * @version $Rev: 2080 $, $Date: 2010-01-26 18:04:19 +0900 (Tue, 26 Jan 2010) $
    31   */
    32  final class MapBackedSet<E> extends AbstractSet<E> implements Serializable {
    33
    34      private static final long serialVersionUID = -6761513279741915432L;
    35
    36      private final Map<E, Boolean> map;
    37
    38      /**
    39       * Creates a new instance which wraps the specified {@code map}.
    40       */
    41      MapBackedSet(Map<E, Boolean> map) {
    42          this.map = map;
    43      }
    44
    45      @Override
    46      public int size() {
    47          return map.size();
    48      }
    49
    50      @Override
    51      public boolean contains(Object o) {
    52          return map.containsKey(o);
    53      }
    54
    55      @Override
    56      public boolean add(E o) {
    57          return map.put(o, Boolean.TRUE) == null;
    58      }
    59
    60      @Override
    61      public boolean remove(Object o) {
    62          return map.remove(o) != null;
    63      }
    64
    65      @Override
    66      public void clear() {
    67          map.clear();
    68      }
    69
    70      @Override
    71      public Iterator<E> iterator() {
    72          return map.keySet().iterator();
    73      }
    74  }