    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 * </p>
    034 *
    035 * @param <K> the type of the keys in the map
    036 * @param <V> the type of the values in the map
    037 *
    038 * @since 4.0
    039 */
    040public class DualLinkedHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
    041
    042    /** Ensure serialization compatibility */
    043    private static final long serialVersionUID = 721969328361810L;
    044
    045    /**
    046     * Creates an empty <code>HashBidiMap</code>.
    047     */
    048    public DualLinkedHashBidiMap() {
    049        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
    050    }
    051
    052    /**
    053     * Constructs a <code>LinkedHashBidiMap</code> and copies the mappings from
    054     * specified <code>Map</code>.
    055     *
    056     * @param map the map whose mappings are to be placed in this map
    057     */
    058    public DualLinkedHashBidiMap(final Map<? extends K, ? extends V> map) {
    059        super(new LinkedHashMap<K, V>(), new LinkedHashMap<V, K>());
    060        putAll(map);
    061    }
    062
    063    /**
    064     * Constructs a <code>LinkedHashBidiMap</code> that decorates the specified maps.
    065     *
    066     * @param normalMap      the normal direction map
    067     * @param reverseMap     the reverse direction map
    068     * @param inverseBidiMap the inverse BidiMap
    069     */
    070    protected DualLinkedHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
    071                                    final BidiMap<V, K> inverseBidiMap) {
    072        super(normalMap, reverseMap, inverseBidiMap);
    073    }
    074
    075    /**
    076     * Creates a new instance of this object.
    077     *
    078     * @param normalMap      the normal direction map
    079     * @param reverseMap     the reverse direction map
    080     * @param inverseBidiMap the inverse BidiMap
    081     * @return new bidi map
    082     */
    083    @Override
    084    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
    085            final BidiMap<K, V> inverseBidiMap) {
    086        return new DualLinkedHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
    087    }
    088
    089    // Serialization
    090    //-----------------------------------------------------------------------
    091    private void writeObject(final ObjectOutputStream out) throws IOException {
    092        out.defaultWriteObject();
    093        out.writeObject(normalMap);
    094    }
    095
    096    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    097        in.defaultReadObject();
    098        normalMap = new LinkedHashMap<>();
    099        reverseMap = new LinkedHashMap<>();
    100        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
    101        final Map<K, V> map = (Map<K, V>) in.readObject();
    102        putAll(map);
    103    }
    104}