    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 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap}
    037 * and the flawed <code>createMap</code> method is ignored.
    038 *
    039 * @param <K> the type of the keys in the map
    040 * @param <V> the type of the values in the map
    041 *
    042 * @since 3.0
    043 */
    044public class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
    045
    046    /** Ensure serialization compatibility */
    047    private static final long serialVersionUID = 721969328361808L;
    048
    049    /**
    050     * Creates an empty <code>HashBidiMap</code>.
    051     */
    052    public DualHashBidiMap() {
    053        super(new HashMap<K, V>(), new HashMap<V, K>());
    054    }
    055
    056    /**
    057     * Constructs a <code>HashBidiMap</code> and copies the mappings from
    058     * specified <code>Map</code>.
    059     *
    060     * @param map  the map whose mappings are to be placed in this map
    061     */
    062    public DualHashBidiMap(final Map<? extends K, ? extends V> map) {
    063        super(new HashMap<K, V>(), new HashMap<V, K>());
    064        putAll(map);
    065    }
    066
    067    /**
    068     * Constructs a <code>HashBidiMap</code> that decorates the specified maps.
    069     *
    070     * @param normalMap  the normal direction map
    071     * @param reverseMap  the reverse direction map
    072     * @param inverseBidiMap  the inverse BidiMap
    073     */
    074    protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
    075                              final BidiMap<V, K> inverseBidiMap) {
    076        super(normalMap, reverseMap, inverseBidiMap);
    077    }
    078
    079    /**
    080     * Creates a new instance of this object.
    081     *
    082     * @param normalMap  the normal direction map
    083     * @param reverseMap  the reverse direction map
    084     * @param inverseBidiMap  the inverse BidiMap
    085     * @return new bidi map
    086     */
    087    @Override
    088    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
    089                                          final BidiMap<K, V> inverseBidiMap) {
    090        return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
    091    }
    092
    093    // Serialization
    094    //-----------------------------------------------------------------------
    095    private void writeObject(final ObjectOutputStream out) throws IOException {
    096        out.defaultWriteObject();
    097        out.writeObject(normalMap);
    098    }
    099
    100    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    101        in.defaultReadObject();
    102        normalMap = new HashMap<>();
    103        reverseMap = new HashMap<>();
    104        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
    105        final Map<K, V> map = (Map<K, V>) in.readObject();
    106        putAll(map);
    107    }
    108
    109}