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 * NOTE: From Commons Collections 3.1, all subclasses will use {@link HashMap} 037 * and the flawed <code>createMap</code> method is ignored. 038 * 039 * @since 3.0 040 * @version $Id: DualHashBidiMap.html 972421 2015-11-14 20:00:04Z tn $ 041 */ 042public class DualHashBidiMap<K, V> extends AbstractDualBidiMap<K, V> implements Serializable { 043 044 /** Ensure serialization compatibility */ 045 private static final long serialVersionUID = 721969328361808L; 046 047 /** 048 * Creates an empty <code>HashBidiMap</code>. 049 */ 050 public DualHashBidiMap() { 051 super(new HashMap<K, V>(), new HashMap<V, K>()); 052 } 053 054 /** 055 * Constructs a <code>HashBidiMap</code> and copies the mappings from 056 * specified <code>Map</code>. 057 * 058 * @param map the map whose mappings are to be placed in this map 059 */ 060 public DualHashBidiMap(final Map<? extends K, ? extends V> map) { 061 super(new HashMap<K, V>(), new HashMap<V, K>()); 062 putAll(map); 063 } 064 065 /** 066 * Constructs a <code>HashBidiMap</code> that decorates the specified maps. 067 * 068 * @param normalMap the normal direction map 069 * @param reverseMap the reverse direction map 070 * @param inverseBidiMap the inverse BidiMap 071 */ 072 protected DualHashBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap, 073 final BidiMap<V, K> inverseBidiMap) { 074 super(normalMap, reverseMap, inverseBidiMap); 075 } 076 077 /** 078 * Creates a new instance of this object. 079 * 080 * @param normalMap the normal direction map 081 * @param reverseMap the reverse direction map 082 * @param inverseBidiMap the inverse BidiMap 083 * @return new bidi map 084 */ 085 @Override 086 protected BidiMap<V, K> createBidiMap(final Map<V, K> normalMap, final Map<K, V> reverseMap, 087 final BidiMap<K, V> inverseBidiMap) { 088 return new DualHashBidiMap<V, K>(normalMap, reverseMap, inverseBidiMap); 089 } 090 091 // Serialization 092 //----------------------------------------------------------------------- 093 private void writeObject(final ObjectOutputStream out) throws IOException { 094 out.defaultWriteObject(); 095 out.writeObject(normalMap); 096 } 097 098 private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException { 099 in.defaultReadObject(); 100 normalMap = new HashMap<K, V>(); 101 reverseMap = new HashMap<V, K>(); 102 @SuppressWarnings("unchecked") // will fail at runtime if stream is incorrect 103 final Map<K, V> map = (Map<K, V>) in.readObject(); 104 putAll(map); 105 } 106 107}