001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.set;
018
019import java.io.Serializable;
020import java.util.Collection;
021import java.util.Iterator;
022import java.util.Map;
023import java.util.Set;
024import java.util.function.Predicate;
025
026/**
027 * Decorates a <code>Map</code> to obtain <code>Set</code> behaviour.
028 * <p>
029 * This class is used to create a <code>Set</code> with the same properties as
030 * the key set of any map. Thus, a ReferenceSet can be created by wrapping a
031 * <code>ReferenceMap</code> in an instance of this class.
032 * </p>
033 * <p>
034 * Most map implementation can be used to create a set by passing in dummy values.
035 * Exceptions include <code>BidiMap</code> implementations, as they require unique values.
036 * </p>
037 *
038 * @param <E> the type of the elements in this set
039 * @param <V> the dummy value type in this map
040 * @since 3.1
041 */
042public final class MapBackedSet<E, V> implements Set<E>, Serializable {
043
044    /** Serialization version */
045    private static final long serialVersionUID = 6723912213766056587L;
046
047    /** The map being used as the backing store */
048    private final Map<E, ? super V> map;
049
050    /** The dummyValue to use */
051    private final V dummyValue;
052
053    /**
054     * Factory method to create a set from a map.
055     *
056     * @param <E> the element type
057     * @param <V> the dummy value type in the map
058     * @param map  the map to decorate, must not be null
059     * @return a new map backed set
060     * @throws NullPointerException if map is null
061     * @since 4.0
062     */
063    public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map) {
064        return mapBackedSet(map, null);
065    }
066
067    /**
068     * Factory method to create a set from a map.
069     *
070     * @param <E> the element type
071     * @param <V> the dummy value type in the map
072     * @param map  the map to decorate, must not be null
073     * @param dummyValue  the dummy value to use
074     * @return a new map backed set
075     * @throws NullPointerException if map is null
076     * @since 4.0
077     */
078    public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map, final V dummyValue) {
079        return new MapBackedSet<>(map, dummyValue);
080    }
081
082    //-----------------------------------------------------------------------
083    /**
084     * Constructor that wraps (not copies).
085     *
086     * @param map  the map to decorate, must not be null
087     * @param dummyValue  the dummy value to use
088     * @throws NullPointerException if map is null
089     */
090    private MapBackedSet(final Map<E, ? super V> map, final V dummyValue) {
091        super();
092        if (map == null) {
093            throw new NullPointerException("The map must not be null");
094        }
095        this.map = map;
096        this.dummyValue = dummyValue;
097    }
098
099    //-----------------------------------------------------------------------
100    @Override
101    public int size() {
102        return map.size();
103    }
104
105    @Override
106    public boolean isEmpty() {
107        return map.isEmpty();
108    }
109
110    @Override
111    public Iterator<E> iterator() {
112        return map.keySet().iterator();
113    }
114
115    @Override
116    public boolean contains(final Object obj) {
117        return map.containsKey(obj);
118    }
119
120    @Override
121    public boolean containsAll(final Collection<?> coll) {
122        return map.keySet().containsAll(coll);
123    }
124
125    @Override
126    public boolean add(final E obj) {
127        final int size = map.size();
128        map.put(obj, dummyValue);
129        return map.size() != size;
130    }
131
132    @Override
133    public boolean addAll(final Collection<? extends E> coll) {
134        final int size = map.size();
135        for (final E e : coll) {
136            map.put(e, dummyValue);
137        }
138        return map.size() != size;
139    }
140
141    @Override
142    public boolean remove(final Object obj) {
143        final int size = map.size();
144        map.remove(obj);
145        return map.size() != size;
146    }
147
148    /**
149     * @since 4.4
150     */
151    @Override
152    public boolean removeIf(Predicate<? super E> filter) {
153        return map.keySet().removeIf(filter);
154    }
155
156    @Override
157    public boolean removeAll(final Collection<?> coll) {
158        return map.keySet().removeAll(coll);
159    }
160
161    @Override
162    public boolean retainAll(final Collection<?> coll) {
163        return map.keySet().retainAll(coll);
164    }
165
166    @Override
167    public void clear() {
168        map.clear();
169    }
170
171    @Override
172    public Object[] toArray() {
173        return map.keySet().toArray();
174    }
175
176    @Override
177    public <T> T[] toArray(final T[] array) {
178        return map.keySet().toArray(array);
179    }
180
181    @Override
182    public boolean equals(final Object obj) {
183        return map.keySet().equals(obj);
184    }
185
186    @Override
187    public int hashCode() {
188        return map.keySet().hashCode();
189    }
190
191}