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/*
 * 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 org.apache.commons.collections4.set;

import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/**
 * Decorates a Map to obtain Set behaviour.
 * 

* This class is used to create a Set with the same properties as * the key set of any map. Thus, a ReferenceSet can be created by wrapping a * ReferenceMap in an instance of this class. *

* Most map implementation can be used to create a set by passing in dummy values. * Exceptions include BidiMap implementations, as they require unique values. * * @since 3.1 * @version $Id: MapBackedSet.java 1686855 2015-06-22 13:00:27Z tn $ */ public final class MapBackedSet implements Set, Serializable { /** Serialization version */ private static final long serialVersionUID = 6723912213766056587L; /** The map being used as the backing store */ private final Map map; /** The dummyValue to use */ private final V dummyValue; /** * Factory method to create a set from a map. * * @param the element type * @param the dummy value type in the map * @param map the map to decorate, must not be null * @return a new map backed set * @throws NullPointerException if map is null * @since 4.0 */ public static MapBackedSet mapBackedSet(final Map map) { return mapBackedSet(map, null); } /** * Factory method to create a set from a map. * * @param the element type * @param the dummy value type in the map * @param map the map to decorate, must not be null * @param dummyValue the dummy value to use * @return a new map backed set * @throws NullPointerException if map is null * @since 4.0 */ public static MapBackedSet mapBackedSet(final Map map, final V dummyValue) { return new MapBackedSet(map, dummyValue); } //----------------------------------------------------------------------- /** * Constructor that wraps (not copies). * * @param map the map to decorate, must not be null * @param dummyValue the dummy value to use * @throws NullPointerException if map is null */ private MapBackedSet(final Map map, final V dummyValue) { super(); if (map == null) { throw new NullPointerException("The map must not be null"); } this.map = map; this.dummyValue = dummyValue; } //----------------------------------------------------------------------- public int size() { return map.size(); } public boolean isEmpty() { return map.isEmpty(); } public Iterator iterator() { return map.keySet().iterator(); } public boolean contains(final Object obj) { return map.containsKey(obj); } public boolean containsAll(final Collection coll) { return map.keySet().containsAll(coll); } public boolean add(final E obj) { final int size = map.size(); map.put(obj, dummyValue); return map.size() != size; } public boolean addAll(final Collection coll) { final int size = map.size(); for (final E e : coll) { map.put(e, dummyValue); } return map.size() != size; } public boolean remove(final Object obj) { final int size = map.size(); map.remove(obj); return map.size() != size; } public boolean removeAll(final Collection coll) { return map.keySet().removeAll(coll); } public boolean retainAll(final Collection coll) { return map.keySet().retainAll(coll); } public void clear() { map.clear(); } public Object[] toArray() { return map.keySet().toArray(); } public T[] toArray(final T[] array) { return map.keySet().toArray(array); } @Override public boolean equals(final Object obj) { return map.keySet().equals(obj); } @Override public int hashCode() { return map.keySet().hashCode(); } }





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