001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect; 018 019import static com.google.common.collect.CollectPreconditions.checkNonnegative; 020 021import com.google.common.annotations.GwtCompatible; 022import com.google.common.annotations.GwtIncompatible; 023import com.google.common.annotations.VisibleForTesting; 024import java.io.IOException; 025import java.io.ObjectInputStream; 026import java.io.ObjectOutputStream; 027import java.util.ArrayList; 028import java.util.Collection; 029import java.util.HashMap; 030import java.util.List; 031import java.util.Map; 032 033/** 034 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store 035 * the values for a given key. A {@link HashMap} associates each key with an 036 * {@link ArrayList} of values. 037 * 038 * <p>When iterating through the collections supplied by this class, the 039 * ordering of values for a given key agrees with the order in which the values 040 * were added. 041 * 042 * <p>This multimap allows duplicate key-value pairs. After adding a new 043 * key-value pair equal to an existing key-value pair, the {@code 044 * ArrayListMultimap} will contain entries for both the new value and the old 045 * value. 046 * 047 * <p>Keys and values may be null. All optional multimap methods are supported, 048 * and all returned views are modifiable. 049 * 050 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link 051 * #replaceValues} all implement {@link java.util.RandomAccess}. 052 * 053 * <p>This class is not threadsafe when any concurrent operations update the 054 * multimap. Concurrent read operations will work correctly. To allow concurrent 055 * update operations, wrap your multimap with a call to {@link 056 * Multimaps#synchronizedListMultimap}. 057 * 058 * <p>See the Guava User Guide article on <a href= 059 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> 060 * {@code Multimap}</a>. 061 * 062 * @author Jared Levy 063 * @since 2.0 064 */ 065@GwtCompatible(serializable = true, emulated = true) 066public final class ArrayListMultimap<K, V> 067 extends ArrayListMultimapGwtSerializationDependencies<K, V> { 068 // Default from ArrayList 069 private static final int DEFAULT_VALUES_PER_KEY = 3; 070 071 @VisibleForTesting transient int expectedValuesPerKey; 072 073 /** 074 * Creates a new, empty {@code ArrayListMultimap} with the default initial capacities. 075 * 076 * <p>This method will soon be deprecated in favor of {@code 077 * MultimapBuilder.hashKeys().arrayListValues().build()}. 078 */ 079 public static <K, V> ArrayListMultimap<K, V> create() { 080 return new ArrayListMultimap<K, V>(); 081 } 082 083 /** 084 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold the specified 085 * numbers of keys and values without resizing. 086 * 087 * <p>This method will soon be deprecated in favor of {@code 088 * MultimapBuilder.hashKeys(expectedKeys).arrayListValues(expectedValuesPerKey).build()}. 089 * 090 * @param expectedKeys the expected number of distinct keys 091 * @param expectedValuesPerKey the expected average number of values per key 092 * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is 093 * negative 094 */ 095 public static <K, V> ArrayListMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) { 096 return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey); 097 } 098 099 /** 100 * Constructs an {@code ArrayListMultimap} with the same mappings as the specified multimap. 101 * 102 * <p>This method will soon be deprecated in favor of {@code 103 * MultimapBuilder.hashKeys().arrayListValues().build(multimap)}. 104 * 105 * @param multimap the multimap whose contents are copied to this multimap 106 */ 107 public static <K, V> ArrayListMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) { 108 return new ArrayListMultimap<K, V>(multimap); 109 } 110 111 private ArrayListMultimap() { 112 super(new HashMap<K, Collection<V>>()); 113 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 114 } 115 116 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) { 117 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys)); 118 checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); 119 this.expectedValuesPerKey = expectedValuesPerKey; 120 } 121 122 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) { 123 this( 124 multimap.keySet().size(), 125 (multimap instanceof ArrayListMultimap) 126 ? ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey 127 : DEFAULT_VALUES_PER_KEY); 128 putAll(multimap); 129 } 130 131 /** 132 * Creates a new, empty {@code ArrayList} to hold the collection of values for 133 * an arbitrary key. 134 */ 135 @Override 136 List<V> createCollection() { 137 return new ArrayList<V>(expectedValuesPerKey); 138 } 139 140 /** 141 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible. 142 * 143 * @deprecated For a {@link ListMultimap} that automatically trims to size, use {@link 144 * ImmutableListMultimap}. If you need a mutable collection, remove the {@code trimToSize} 145 * call, or switch to a {@code HashMap<K, ArrayList<V>>}. This method is scheduled for removal 146 * in April 2019. 147 */ 148 @Deprecated 149 public void trimToSize() { 150 for (Collection<V> collection : backingMap().values()) { 151 ArrayList<V> arrayList = (ArrayList<V>) collection; 152 arrayList.trimToSize(); 153 } 154 } 155 156 /** 157 * @serialData expectedValuesPerKey, number of distinct keys, and then for 158 * each distinct key: the key, number of values for that key, and the 159 * key's values 160 */ 161 @GwtIncompatible // java.io.ObjectOutputStream 162 private void writeObject(ObjectOutputStream stream) throws IOException { 163 stream.defaultWriteObject(); 164 Serialization.writeMultimap(this, stream); 165 } 166 167 @GwtIncompatible // java.io.ObjectOutputStream 168 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException { 169 stream.defaultReadObject(); 170 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 171 int distinctKeys = Serialization.readCount(stream); 172 Map<K, Collection<V>> map = Maps.newHashMap(); 173 setMap(map); 174 Serialization.populateMultimap(this, stream, distinctKeys); 175 } 176 177 @GwtIncompatible // Not needed in emulated source. 178 private static final long serialVersionUID = 0; 179}