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.LinkedHashMap;
024import java.util.Map;
025
026import org.apache.commons.collections4.BidiMap;
027
028/**
029 * Implementation of <code>BidiMap</code> that uses two <code>LinkedHashMap</code> instances.
030 * <p>
031 * Two <code>LinkedHashMap</code> instances are used in this class.
032 * This provides fast lookups at the expense of storing two sets of map entries and two linked lists.
033 *
034 * @param <K> the type of the keys in the map
035 * @param <V> the type of the values in the map
036 *
037 * @since 4.0
038 */
039public class DualLinkedHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
040
041    /** Ensure serialization compatibility */
042    private static final long serialVersionUID = 721969328361810L;
043
044    /**
045     * Creates an empty <code>HashBidiMap</code>.
046     */
047    public DualLinkedHashBidiMap() {
048        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
049    }
050
051    /**
052     * Constructs a <code>LinkedHashBidiMap</code> and copies the mappings from
053     * specified <code>Map</code>.
054     *
055     * @param map the map whose mappings are to be placed in this map
056     */
057    public DualLinkedHashBidiMap(final Map<? extends K, ? extends V> map) {
058        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
059        putAll(map);
060    }
061
062    /**
063     * Constructs a <code>LinkedHashBidiMap</code> that decorates the specified maps.
064     *
065     * @param normalMap      the normal direction map
066     * @param reverseMap     the reverse direction map
067     * @param inverseBidiMap the inverse BidiMap
068     */
069    protected DualLinkedHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
070                                    final BidiMap<V, K> inverseBidiMap) {
071        super(normalMap, reverseMap, inverseBidiMap);
072    }
073
074    /**
075     * Creates a new instance of this object.
076     *
077     * @param normalMap      the normal direction map
078     * @param reverseMap     the reverse direction map
079     * @param inverseBidiMap the inverse BidiMap
080     * @return new bidi map
081     */
082    @Override
083    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
084            final BidiMap<K, V> inverseBidiMap) {
085        return new DualLinkedHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
086    }
087
088    // Serialization
089    //-----------------------------------------------------------------------
090    private void writeObject(final ObjectOutputStream out) throws IOException {
091        out.defaultWriteObject();
092        out.writeObject(normalMap);
093    }
094
095    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
096        in.defaultReadObject();
097        normalMap = new LinkedHashMap<>();
098        reverseMap = new LinkedHashMap<>();
099        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
100        final Map<K, V> map = (Map<K, V>) in.readObject();
101        putAll(map);
102    }
103}