    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 *      https://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.Objects;
    024import java.util.Set;
    025import java.util.function.Predicate;
    026
    027/**
    028 * Decorates a {@code Map} to obtain {@code Set} behavior.
    029 * <p>
    030 * This class is used to create a {@code Set} with the same properties as
    031 * the key set of any map. Thus, a ReferenceSet can be created by wrapping a
    032 * {@code ReferenceMap} in an instance of this class.
    033 * </p>
    034 * <p>
    035 * Most map implementation can be used to create a set by passing in dummy values.
    036 * Exceptions include {@code BidiMap} implementations, as they require unique values.
    037 * </p>
    038 *
    039 * @param <E> The type of the elements in this set
    040 * @param <V> The dummy value type in this map
    041 * @since 3.1
    042 */
    043public final class MapBackedSet<E, V> implements Set<E>, Serializable {
    044
    045    /** Serialization version */
    046    private static final long serialVersionUID = 6723912213766056587L;
    047
    048    /**
    049     * Factory method to create a set from a map.
    050     *
    051     * @param <E> The element type
    052     * @param <V> The dummy value type in the map
    053     * @param map  The map to decorate, must not be null
    054     * @return A new map backed set
    055     * @throws NullPointerException if map is null
    056     * @since 4.0
    057     */
    058    public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map) {
    059        return mapBackedSet(map, null);
    060    }
    061
    062    /**
    063     * Factory method to create a set from a map.
    064     *
    065     * @param <E> The element type
    066     * @param <V> The dummy value type in the map
    067     * @param map  The map to decorate, must not be null
    068     * @param dummyValue  The dummy value to use
    069     * @return A new map backed set
    070     * @throws NullPointerException if map is null
    071     * @since 4.0
    072     */
    073    public static <E, V> MapBackedSet<E, V> mapBackedSet(final Map<E, ? super V> map, final V dummyValue) {
    074        return new MapBackedSet<>(map, dummyValue);
    075    }
    076
    077    /** The map being used as the backing store */
    078    private final Map<E, ? super V> map;
    079
    080    /** The dummyValue to use */
    081    private final V dummyValue;
    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        this.map = Objects.requireNonNull(map, "map");
    092        this.dummyValue = dummyValue;
    093    }
    094
    095    @Override
    096    public boolean add(final E obj) {
    097        final int size = map.size();
    098        map.put(obj, dummyValue);
    099        return map.size() != size;
    100    }
    101
    102    @Override
    103    public boolean addAll(final Collection<? extends E> coll) {
    104        final int size = map.size();
    105        for (final E e : coll) {
    106            map.put(e, dummyValue);
    107        }
    108        return map.size() != size;
    109    }
    110
    111    @Override
    112    public void clear() {
    113        map.clear();
    114    }
    115
    116    @Override
    117    public boolean contains(final Object obj) {
    118        return map.containsKey(obj);
    119    }
    120
    121    @Override
    122    public boolean containsAll(final Collection<?> coll) {
    123        return map.keySet().containsAll(coll);
    124    }
    125
    126    @Override
    127    public boolean equals(final Object obj) {
    128        return map.keySet().equals(obj);
    129    }
    130
    131    @Override
    132    public int hashCode() {
    133        return map.keySet().hashCode();
    134    }
    135
    136    @Override
    137    public boolean isEmpty() {
    138        return map.isEmpty();
    139    }
    140
    141    @Override
    142    public Iterator<E> iterator() {
    143        return map.keySet().iterator();
    144    }
    145
    146    @Override
    147    public boolean remove(final Object obj) {
    148        final int size = map.size();
    149        map.remove(obj);
    150        return map.size() != size;
    151    }
    152
    153    @Override
    154    public boolean removeAll(final Collection<?> coll) {
    155        return map.keySet().removeAll(coll);
    156    }
    157
    158    /**
    159     * @since 4.4
    160     */
    161    @Override
    162    public boolean removeIf(final Predicate<? super E> filter) {
    163        return map.keySet().removeIf(filter);
    164    }
    165
    166    @Override
    167    public boolean retainAll(final Collection<?> coll) {
    168        return map.keySet().retainAll(coll);
    169    }
    170
    171    @Override
    172    public int size() {
    173        return map.size();
    174    }
    175
    176    @Override
    177    public Object[] toArray() {
    178        return map.keySet().toArray();
    179    }
    180
    181    @Override
    182    public <T> T[] toArray(final T[] array) {
    183        return map.keySet().toArray(array);
    184    }
    185
    186}