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.bidimap;
018
019import java.io.IOException;
020import java.io.ObjectInputStream;
021import java.io.ObjectOutputStream;
022import java.io.Serializable;
023import java.util.HashMap;
024import java.util.Map;
025
026import org.apache.commons.collections4.BidiMap;
027
028/**
029 * Implementation of {@link BidiMap} that uses two {@link HashMap} instances.
030 * <p>
031 * Two {@link HashMap} instances are used in this class.
032 * This provides fast lookups at the expense of storing two sets of map entries.
033 * Commons Collections would welcome the addition of a direct hash-based
034 * implementation of the {@link BidiMap} interface.
035 * </p>
036 * <p>
037 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap}
038 * and the flawed <code>createMap</code> method is ignored.
039 * </p>
040 *
041 * @param <K> the type of the keys in the map
042 * @param <V> the type of the values in the map
043 *
044 * @since 3.0
045 */
046public class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
047
048    /** Ensure serialization compatibility */
049    private static final long serialVersionUID = 721969328361808L;
050
051    /**
052     * Creates an empty <code>HashBidiMap</code>.
053     */
054    public DualHashBidiMap() {
055        super(new HashMap<K, V>(), new HashMap<V, K>());
056    }
057
058    /**
059     * Constructs a <code>HashBidiMap</code> and copies the mappings from
060     * specified <code>Map</code>.
061     *
062     * @param map  the map whose mappings are to be placed in this map
063     */
064    public DualHashBidiMap(final Map<? extends K, ? extends V> map) {
065        super(new HashMap<K, V>(), new HashMap<V, K>());
066        putAll(map);
067    }
068
069    /**
070     * Constructs a <code>HashBidiMap</code> that decorates the specified maps.
071     *
072     * @param normalMap  the normal direction map
073     * @param reverseMap  the reverse direction map
074     * @param inverseBidiMap  the inverse BidiMap
075     */
076    protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
077                              final BidiMap<V, K> inverseBidiMap) {
078        super(normalMap, reverseMap, inverseBidiMap);
079    }
080
081    /**
082     * Creates a new instance of this object.
083     *
084     * @param normalMap  the normal direction map
085     * @param reverseMap  the reverse direction map
086     * @param inverseBidiMap  the inverse BidiMap
087     * @return new bidi map
088     */
089    @Override
090    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
091                                          final BidiMap<K, V> inverseBidiMap) {
092        return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
093    }
094
095    // Serialization
096    //-----------------------------------------------------------------------
097    private void writeObject(final ObjectOutputStream out) throws IOException {
098        out.defaultWriteObject();
099        out.writeObject(normalMap);
100    }
101
102    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
103        in.defaultReadObject();
104        normalMap = new HashMap<>();
105        reverseMap = new HashMap<>();
106        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
107        final Map<K, V> map = (Map<K, V>) in.readObject();
108        putAll(map);
109    }
110
111}