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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the 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  final class MapBackedSet<E> extends AbstractSet<E> implements Serializable {
    28
    29      private static final long serialVersionUID = -6761513279741915432L;
    30
    31      private final Map<E, Boolean> map;
    32
    33      /**
    34       * Creates a new instance which wraps the specified {@code map}.
    35       */
    36      MapBackedSet(Map<E, Boolean> map) {
    37          this.map = map;
    38      }
    39
    40      @Override
    41      public int size() {
    42          return map.size();
    43      }
    44
    45      @Override
    46      public boolean contains(Object o) {
    47          return map.containsKey(o);
    48      }
    49
    50      @Override
    51      public boolean add(E o) {
    52          return map.put(o, Boolean.TRUE) == null;
    53      }
    54
    55      @Override
    56      public boolean remove(Object o) {
    57          return map.remove(o) != null;
    58      }
    59
    60      @Override
    61      public void clear() {
    62          map.clear();
    63      }
    64
    65      @Override
    66      public Iterator<E> iterator() {
    67          return map.keySet().iterator();
    68      }
    69  }