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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.openjpa.lib.util.collections;

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

/**
 * Implementation of {@link BidiMap} that uses two {@link HashMap} instances.
 * 
 * Two {@link 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 {@link BidiMap} interface.
 * 
 * 
 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap}
 * and the flawed createMap method is ignored.
 * 
 *
 * @param  the type of the keys in the map
 * @param  the type of the values in the map
 *
 * @since 3.0
 */
public class DualHashBidiMap extends AbstractDualBidiMap implements Serializable {

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

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

    /**
     * Constructs a HashBidiMap and copies the mappings from
     * specified Map.
     *
     * @param map  the map whose mappings are to be placed in this map
     */
    public DualHashBidiMap(final Map map) {
        super(new HashMap<>(), new HashMap<>());
        putAll(map);
    }

    /**
     * Constructs a HashBidiMap that decorates the specified maps.
     *
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @param inverseBidiMap  the inverse BidiMap
     */
    protected DualHashBidiMap(final Map normalMap, final Map reverseMap,
                              final BidiMap inverseBidiMap) {
        super(normalMap, reverseMap, inverseBidiMap);
    }

    /**
     * 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
     */
    @Override
    protected BidiMap createBidiMap(final Map normalMap, final Map reverseMap,
                                          final BidiMap inverseBidiMap) {
        return new DualHashBidiMap<>(normalMap, reverseMap, inverseBidiMap);
    }

    // Serialization
    //-----------------------------------------------------------------------
    private void writeObject(final ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeObject(normalMap);
    }

    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        normalMap = new HashMap<>();
        reverseMap = new HashMap<>();
        @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect
        final Map map = (Map) in.readObject();
        putAll(map);
    }

}