1/* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package com.google.common.collect; 18 19import static com.google.common.collect.CollectPreconditions.checkNonnegative; 20 21import com.google.common.annotations.GwtCompatible; 22import com.google.common.annotations.GwtIncompatible; 23import com.google.common.annotations.VisibleForTesting; 24 25import java.io.IOException; 26import java.io.ObjectInputStream; 27import java.io.ObjectOutputStream; 28import java.util.ArrayList; 29import java.util.Collection; 30import java.util.HashMap; 31import java.util.List; 32import java.util.Map; 33 34/** 35 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store 36 * the values for a given key. A {@link HashMap} associates each key with an 37 * {@link ArrayList} of values. 38 * 39 * <p>When iterating through the collections supplied by this class, the 40 * ordering of values for a given key agrees with the order in which the values 41 * were added. 42 * 43 * <p>This multimap allows duplicate key-value pairs. After adding a new 44 * key-value pair equal to an existing key-value pair, the {@code 45 * ArrayListMultimap} will contain entries for both the new value and the old 46 * value. 47 * 48 * <p>Keys and values may be null. All optional multimap methods are supported, 49 * and all returned views are modifiable. 50 * 51 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link 52 * #replaceValues} all implement {@link java.util.RandomAccess}. 53 * 54 * <p>This class is not threadsafe when any concurrent operations update the 55 * multimap. Concurrent read operations will work correctly. To allow concurrent 56 * update operations, wrap your multimap with a call to {@link 57 * Multimaps#synchronizedListMultimap}. 58 * 59 * <p>See the Guava User Guide article on <a href= 60 * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap"> 61 * {@code Multimap}</a>. 62 * 63 * @author Jared Levy 64 * @since 2.0 (imported from Google Collections Library) 65 */ 66@GwtCompatible(serializable = true, emulated = true) 67public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> { 68 // Default from ArrayList 69 private static final int DEFAULT_VALUES_PER_KEY = 3; 70 71 @VisibleForTesting transient int expectedValuesPerKey; 72 73 /** 74 * Creates a new, empty {@code ArrayListMultimap} with the default initial 75 * capacities. 76 */ 77 public static <K, V> ArrayListMultimap<K, V> create() { 78 return new ArrayListMultimap<K, V>(); 79 } 80 81 /** 82 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold 83 * the specified numbers of keys and values without resizing. 84 * 85 * @param expectedKeys the expected number of distinct keys 86 * @param expectedValuesPerKey the expected average number of values per key 87 * @throws IllegalArgumentException if {@code expectedKeys} or {@code 88 * expectedValuesPerKey} is negative 89 */ 90 public static <K, V> ArrayListMultimap<K, V> create( 91 int expectedKeys, int expectedValuesPerKey) { 92 return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey); 93 } 94 95 /** 96 * Constructs an {@code ArrayListMultimap} with the same mappings as the 97 * specified multimap. 98 * 99 * @param multimap the multimap whose contents are copied to this multimap 100 */ 101 public static <K, V> ArrayListMultimap<K, V> create( 102 Multimap<? extends K, ? extends V> multimap) { 103 return new ArrayListMultimap<K, V>(multimap); 104 } 105 106 private ArrayListMultimap() { 107 super(new HashMap<K, Collection<V>>()); 108 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 109 } 110 111 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) { 112 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys)); 113 checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); 114 this.expectedValuesPerKey = expectedValuesPerKey; 115 } 116 117 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) { 118 this(multimap.keySet().size(), 119 (multimap instanceof ArrayListMultimap) ? 120 ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey : 121 DEFAULT_VALUES_PER_KEY); 122 putAll(multimap); 123 } 124 125 /** 126 * Creates a new, empty {@code ArrayList} to hold the collection of values for 127 * an arbitrary key. 128 */ 129 @Override List<V> createCollection() { 130 return new ArrayList<V>(expectedValuesPerKey); 131 } 132 133 /** 134 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible. 135 */ 136 public void trimToSize() { 137 for (Collection<V> collection : backingMap().values()) { 138 ArrayList<V> arrayList = (ArrayList<V>) collection; 139 arrayList.trimToSize(); 140 } 141 } 142 143 /** 144 * @serialData expectedValuesPerKey, number of distinct keys, and then for 145 * each distinct key: the key, number of values for that key, and the 146 * key's values 147 */ 148 @GwtIncompatible("java.io.ObjectOutputStream") 149 private void writeObject(ObjectOutputStream stream) throws IOException { 150 stream.defaultWriteObject(); 151 stream.writeInt(expectedValuesPerKey); 152 Serialization.writeMultimap(this, stream); 153 } 154 155 @GwtIncompatible("java.io.ObjectOutputStream") 156 private void readObject(ObjectInputStream stream) 157 throws IOException, ClassNotFoundException { 158 stream.defaultReadObject(); 159 expectedValuesPerKey = stream.readInt(); 160 int distinctKeys = Serialization.readCount(stream); 161 Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys); 162 setMap(map); 163 Serialization.populateMultimap(this, stream, distinctKeys); 164 } 165 166 @GwtIncompatible("Not needed in emulated source.") 167 private static final long serialVersionUID = 0; 168} 169