    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.multimap;
    018
    019import java.util.Collections;
    020import java.util.Map;
    021import java.util.Set;
    022
    023import org.apache.commons.collections4.SetUtils;
    024import org.apache.commons.collections4.SetValuedMap;
    025
    026/**
    027 * Abstract implementation of the {@link SetValuedMap} interface to simplify the
    028 * creation of subclass implementations.
    029 * <p>
    030 * Subclasses specify a Map implementation to use as the internal storage and
    031 * the Set implementation to use as values.
    032 * </p>
    033 *
    034 * @param <K> the type of the keys in this map
    035 * @param <V> the type of the values in this map
    036 * @since 4.1
    037 */
    038public abstract class AbstractSetValuedMap<K, V> extends AbstractMultiValuedMap<K, V>
    039    implements SetValuedMap<K, V> {
    040
    041    /**
    042     * Wrapped set to handle add and remove on the collection returned by
    043     * {@code get(Object)}.
    044     */
    045    private final class WrappedSet extends WrappedCollection implements Set<V> {
    046
    047        WrappedSet(final K key) {
    048            super(key);
    049        }
    050
    051        @Override
    052        public boolean equals(final Object other) {
    053            final Set<V> set = (Set<V>) getMapping();
    054            if (set == null) {
    055                return Collections.emptySet().equals(other);
    056            }
    057            if (!(other instanceof Set)) {
    058                return false;
    059            }
    060            final Set<?> otherSet = (Set<?>) other;
    061            return SetUtils.isEqualSet(set, otherSet);
    062        }
    063
    064        @Override
    065        public int hashCode() {
    066            final Set<V> set = (Set<V>) getMapping();
    067            return SetUtils.hashCodeForSet(set);
    068        }
    069
    070    }
    071
    072    /**
    073     * Constructor needed for subclass serialisation.
    074     */
    075    protected AbstractSetValuedMap() {
    076    }
    077
    078    /**
    079     * A constructor that wraps, not copies
    080     *
    081     * @param map  the map to wrap, must not be null
    082     * @throws NullPointerException if the map is null
    083     */
    084    protected AbstractSetValuedMap(final Map<K, ? extends Set<V>> map) {
    085        super(map);
    086    }
    087
    088    /**
    089     * Creates a new value collection using the provided factory.
    090     * @return a new set
    091     */
    092    @Override
    093    protected abstract Set<V> createCollection();
    094
    095    /**
    096     * Gets the set of values associated with the specified key. This would
    097     * return an empty set in case the mapping is not present
    098     *
    099     * @param key  the key to retrieve
    100     * @return the {@code Set} of values, will return an empty
    101     *   {@code Set} for no mapping
    102     */
    103    @Override
    104    public Set<V> get(final K key) {
    105        return wrappedCollection(key);
    106    }
    107
    108    @Override
    109    @SuppressWarnings("unchecked")
    110    protected Map<K, Set<V>> getMap() {
    111        return (Map<K, Set<V>>) super.getMap();
    112    }
    113
    114    /**
    115     * Removes all values associated with the specified key.
    116     * <p>
    117     * A subsequent {@code get(Object)} would return an empty set.
    118     * </p>
    119     *
    120     * @param key the key to remove values from
    121     * @return the {@code Set} of values removed, will return an empty,
    122     *   unmodifiable set for no mapping found.
    123     */
    124    @Override
    125    public Set<V> remove(final Object key) {
    126        return SetUtils.emptyIfNull(getMap().remove(key));
    127    }
    128
    129    @Override
    130    Set<V> wrappedCollection(final K key) {
    131        return new WrappedSet(key);
    132    }
    133}