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 * Implements {@link BidiMap} with 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} 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 * @since 3.0
044 */
045public class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
046
047    /** Ensure serialization compatibility */
048    private static final long serialVersionUID = 721969328361808L;
049
050    /**
051     * Creates an empty {@code HashBidiMap}.
052     */
053    public DualHashBidiMap() {
054        super(new HashMap<>(), new HashMap<>());
055    }
056
057    /**
058     * Constructs a {@code HashBidiMap} and copies the mappings from
059     * specified {@code Map}.
060     *
061     * @param map  the map whose mappings are to be placed in this map
062     */
063    public DualHashBidiMap(final Map<? extends K, ? extends V> map) {
064        super(new HashMap<>(), new HashMap<>());
065        putAll(map);
066    }
067
068    /**
069     * Constructs a {@code HashBidiMap} that decorates the specified maps.
070     *
071     * @param normalMap  the normal direction map
072     * @param reverseMap  the reverse direction map
073     * @param inverseBidiMap  the inverse BidiMap
074     */
075    protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
076                              final BidiMap<V, K> inverseBidiMap) {
077        super(normalMap, reverseMap, inverseBidiMap);
078    }
079
080    /**
081     * Creates a new instance of this object.
082     *
083     * @param normalMap  the normal direction map
084     * @param reverseMap  the reverse direction map
085     * @param inverseBidiMap  the inverse BidiMap
086     * @return new bidi map
087     */
088    @Override
089    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
090                                          final BidiMap<K, V> inverseBidiMap) {
091        return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
092    }
093
094    /**
095     * Deserializes an instance from an ObjectInputStream.
096     *
097     * @param in The source ObjectInputStream.
098     * @throws IOException            Any of the usual Input/Output related exceptions.
099     * @throws ClassNotFoundException A class of a serialized object cannot be found.
100     */
101    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
102        in.defaultReadObject();
103        normalMap = new HashMap<>();
104        reverseMap = new HashMap<>();
105        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
106        final Map<K, V> map = (Map<K, V>) in.readObject();
107        putAll(map);
108    }
109
110    /**
111     * Serializes this object to an ObjectOutputStream.
112     *
113     * @param out the target ObjectOutputStream.
114     * @throws IOException thrown when an I/O errors occur writing to the target stream.
115     */
116    private void writeObject(final ObjectOutputStream out) throws IOException {
117        out.defaultWriteObject();
118        out.writeObject(normalMap);
119    }
120
121}