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 * Implements {@link BidiMap} with 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} 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}. 053 */ 054 public DualHashBidiMap() { 055 super(new HashMap<>(), new HashMap<>()); 056 } 057 058 /** 059 * Constructs a {@code HashBidiMap} and copies the mappings from 060 * specified {@code Map}. 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<>(), new HashMap<>()); 066 putAll(map); 067 } 068 069 /** 070 * Constructs a {@code HashBidiMap} 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 private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException { 096 in.defaultReadObject(); 097 normalMap = new HashMap<>(); 098 reverseMap = new HashMap<>(); 099 @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect 100 final Map<K, V> map = (Map<K, V>) in.readObject(); 101 putAll(map); 102 } 103 104 // Serialization 105 private void writeObject(final ObjectOutputStream out) throws IOException { 106 out.defaultWriteObject(); 107 out.writeObject(normalMap); 108 } 109 110}