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 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections.bidimap;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.collections.BidiMap;

Implementation of BidiMap that uses two HashMap instances.

Two HashMap instances are used in this class.
This provides fast lookups at the expense of storing two sets of map entries.
Commons Collections would welcome the addition of a direct hash-based
implementation of the BidiMap interface.

NOTE: From Commons Collections 3.1, all subclasses will use HashMap
and the flawed createMap method is ignored.
Author:
Matthew Hawthorne, Stephen Colebourne
Since:
Commons Collections 3.0
Version:
$Id: DualHashBidiMap.java 646777 2008-04-10 12:33:15Z niallp $/**
 * Implementation of <code>BidiMap</code> that uses two <code>HashMap</code> instances.
 * <p>
 * Two <code>HashMap</code> instances are used in this class.
 * This provides fast lookups at the expense of storing two sets of map entries.
 * Commons Collections would welcome the addition of a direct hash-based
 * implementation of the <code>BidiMap</code> interface.
 * <p>
 * NOTE: From Commons Collections 3.1, all subclasses will use <code>HashMap</code>
 * and the flawed <code>createMap</code> method is ignored.
 * 
 * @since Commons Collections 3.0
 * @version $Id: DualHashBidiMap.java 646777 2008-04-10 12:33:15Z niallp $
 * 
 * @author Matthew Hawthorne
 * @author Stephen Colebourne
 */
public class DualHashBidiMap
        extends AbstractDualBidiMap implements Serializable {

    
Ensure serialization compatibility /** Ensure serialization compatibility */
    private static final long serialVersionUID = 721969328361808L;

    
Creates an empty HashBidiMap.
/**
     * Creates an empty <code>HashBidiMap</code>.
     */
    public DualHashBidiMap() {
        super(new HashMap(), new HashMap());
    }

    
Constructs a HashBidiMap and copies the mappings from
specified Map.  
Params:
map –  the map whose mappings are to be placed in this map/** 
     * Constructs a <code>HashBidiMap</code> and copies the mappings from
     * specified <code>Map</code>.  
     *
     * @param map  the map whose mappings are to be placed in this map
     */
    public DualHashBidiMap(Map map) {
        super(new HashMap(), new HashMap());
        putAll(map);
    }
    
    
Constructs a HashBidiMap that decorates the specified maps.
Params:
normalMap –  the normal direction map
reverseMap –  the reverse direction map
inverseBidiMap –  the inverse BidiMap/** 
     * Constructs a <code>HashBidiMap</code> that decorates the specified maps.
     *
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @param inverseBidiMap  the inverse BidiMap
     */
    protected DualHashBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) {
        super(normalMap, reverseMap, inverseBidiMap);
    }

    
Creates a new instance of this object.
Params:
normalMap –  the normal direction map
reverseMap –  the reverse direction map
inverseBidiMap –  the inverse BidiMap
Returns:
new bidi map/**
     * Creates a new instance of this object.
     * 
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @param inverseBidiMap  the inverse BidiMap
     * @return new bidi map
     */
    protected BidiMap createBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) {
        return new DualHashBidiMap(normalMap, reverseMap, inverseBidiMap);
    }

    // Serialization
    //-----------------------------------------------------------------------
    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeObject(maps[0]);
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        maps[0] = new HashMap();
        maps[1] = new HashMap();
        Map map = (Map) in.readObject();
        putAll(map);
    }

}