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 * @version $Id: DualLinkedHashBidiMap.html 887892 2013-11-24 13:43:45Z tn $
035 * @since 4.0
036 */
037public class DualLinkedHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
038
039    /** Ensure serialization compatibility */
040    private static final long serialVersionUID = 721969328361810L;
041
042    /**
043     * Creates an empty <code>HashBidiMap</code>.
044     */
045    public DualLinkedHashBidiMap() {
046        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
047    }
048
049    /**
050     * Constructs a <code>LinkedHashBidiMap</code> and copies the mappings from
051     * specified <code>Map</code>.
052     *
053     * @param map the map whose mappings are to be placed in this map
054     */
055    public DualLinkedHashBidiMap(final Map<? extends K, ? extends V> map) {
056        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
057        putAll(map);
058    }
059
060    /**
061     * Constructs a <code>LinkedHashBidiMap</code> that decorates the specified maps.
062     *
063     * @param normalMap      the normal direction map
064     * @param reverseMap     the reverse direction map
065     * @param inverseBidiMap the inverse BidiMap
066     */
067    protected DualLinkedHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
068                                    final BidiMap<V, K> inverseBidiMap) {
069        super(normalMap, reverseMap, inverseBidiMap);
070    }
071
072    /**
073     * Creates a new instance of this object.
074     *
075     * @param normalMap      the normal direction map
076     * @param reverseMap     the reverse direction map
077     * @param inverseBidiMap the inverse BidiMap
078     * @return new bidi map
079     */
080    @Override
081    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
082            final BidiMap<K, V> inverseBidiMap) {
083        return new DualLinkedHashBidiMap<V, K>(normalMap, reverseMap, inverseBidiMap);
084    }
085
086    // Serialization
087    //-----------------------------------------------------------------------
088    private void writeObject(final ObjectOutputStream out) throws IOException {
089        out.defaultWriteObject();
090        out.writeObject(normalMap);
091    }
092
093    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
094        in.defaultReadObject();
095        normalMap = new LinkedHashMap<K, V>();
096        reverseMap = new LinkedHashMap<V, K>();
097        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
098        final Map<K, V> map = (Map<K, V>) in.readObject();
099        putAll(map);
100    }
101}