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     */
017    package org.apache.commons.collections.bidimap;
018    
019    import java.io.IOException;
020    import java.io.ObjectInputStream;
021    import java.io.ObjectOutputStream;
022    import java.io.Serializable;
023    import java.util.HashMap;
024    import java.util.Map;
025    
026    import org.apache.commons.collections.BidiMap;
027    
028    /**
029     * Implementation of <code>BidiMap</code> that uses two <code>HashMap</code> instances.
030     * <p>
031     * Two <code>HashMap</code> 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 <code>BidiMap</code> interface.
035     * <p>
036     * NOTE: From Commons Collections 3.1, all subclasses will use <code>HashMap</code>
037     * and the flawed <code>createMap</code> method is ignored.
038     * 
039     * @since Commons Collections 3.0
040     * @version $Id: DualHashBidiMap.java 646777 2008-04-10 12:33:15Z niallp $
041     * 
042     * @author Matthew Hawthorne
043     * @author Stephen Colebourne
044     */
045    public class DualHashBidiMap
046            extends AbstractDualBidiMap 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(), new HashMap());
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(Map map) {
065            super(new HashMap(), new HashMap());
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(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) {
077            super(normalMap, reverseMap, inverseBidiMap);
078        }
079    
080        /**
081         * Creates a new instance of this object.
082         * 
083         * @param normalMap  the normal direction map
084         * @param reverseMap  the reverse direction map
085         * @param inverseBidiMap  the inverse BidiMap
086         * @return new bidi map
087         */
088        protected BidiMap createBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) {
089            return new DualHashBidiMap(normalMap, reverseMap, inverseBidiMap);
090        }
091    
092        // Serialization
093        //-----------------------------------------------------------------------
094        private void writeObject(ObjectOutputStream out) throws IOException {
095            out.defaultWriteObject();
096            out.writeObject(maps[0]);
097        }
098    
099        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
100            in.defaultReadObject();
101            maps[0] = new HashMap();
102            maps[1] = new HashMap();
103            Map map = (Map) in.readObject();
104            putAll(map);
105        }
106    
107    }