    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 * <p>
    037 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap}
    038 * and the flawed <code>createMap</code> 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 *
    044 * @since 3.0
    045 */
    046public class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable {
    047
    048    /** Ensure serialization compatibility */
    049    private static final long serialVersionUID = 721969328361808L;
    050
    051    /**
    052     * Creates an empty <code>HashBidiMap</code>.
    053     */
    054    public DualHashBidiMap() {
    055        super(new HashMap<K, V>(), new HashMap<V, K>());
    056    }
    057
    058    /**
    059     * Constructs a <code>HashBidiMap</code> and copies the mappings from
    060     * specified <code>Map</code>.
    061     *
    062     * @param map  the map whose mappings are to be placed in this map
    063     */
    064    public DualHashBidiMap(final Map<? extends K, ? extends V> map) {
    065        super(new HashMap<K, V>(), new HashMap<V, K>());
    066        putAll(map);
    067    }
    068
    069    /**
    070     * Constructs a <code>HashBidiMap</code> that decorates the specified maps.
    071     *
    072     * @param normalMap  the normal direction map
    073     * @param reverseMap  the reverse direction map
    074     * @param inverseBidiMap  the inverse BidiMap
    075     */
    076    protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
    077                              final BidiMap<V, K> inverseBidiMap) {
    078        super(normalMap, reverseMap, inverseBidiMap);
    079    }
    080
    081    /**
    082     * Creates a new instance of this object.
    083     *
    084     * @param normalMap  the normal direction map
    085     * @param reverseMap  the reverse direction map
    086     * @param inverseBidiMap  the inverse BidiMap
    087     * @return new bidi map
    088     */
    089    @Override
    090    protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap,
    091                                          final BidiMap<K, V> inverseBidiMap) {
    092        return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
    093    }
    094
    095    // Serialization
    096    //-----------------------------------------------------------------------
    097    private void writeObject(final ObjectOutputStream out) throws IOException {
    098        out.defaultWriteObject();
    099        out.writeObject(normalMap);
    100    }
    101
    102    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    103        in.defaultReadObject();
    104        normalMap = new HashMap<>();
    105        reverseMap = new HashMap<>();
    106        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
    107        final Map<K, V> map = (Map<K, V>) in.readObject();
    108        putAll(map);
    109    }
    110
    111}