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 17 package com.google.common.collect; 18 19 import static com.google.common.base.Preconditions.checkArgument; 20 21 import com.google.common.annotations.GwtCompatible; 22 import com.google.common.annotations.GwtIncompatible; 23 import com.google.common.annotations.VisibleForTesting; 24 25 import java.io.IOException; 26 import java.io.ObjectInputStream; 27 import java.io.ObjectOutputStream; 28 import java.util.ArrayList; 29 import java.util.Collection; 30 import java.util.HashMap; 31 import java.util.List; 32 import 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 * @author Jared Levy 60 * @since 2.0 (imported from Google Collections Library) 61 */ 62 @GwtCompatible(serializable = true, emulated = true) 63 public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> { 64 // Default from ArrayList 65 private static final int DEFAULT_VALUES_PER_KEY = 10; 66 67 @VisibleForTesting transient int expectedValuesPerKey; 68 69 /** 70 * Creates a new, empty {@code ArrayListMultimap} with the default initial 71 * capacities. 72 */ 73 public static <K, V> ArrayListMultimap<K, V> create() { 74 return new ArrayListMultimap<K, V>(); 75 } 76 77 /** 78 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold 79 * the specified numbers of keys and values without resizing. 80 * 81 * @param expectedKeys the expected number of distinct keys 82 * @param expectedValuesPerKey the expected average number of values per key 83 * @throws IllegalArgumentException if {@code expectedKeys} or {@code 84 * expectedValuesPerKey} is negative 85 */ 86 public static <K, V> ArrayListMultimap<K, V> create( 87 int expectedKeys, int expectedValuesPerKey) { 88 return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey); 89 } 90 91 /** 92 * Constructs an {@code ArrayListMultimap} with the same mappings as the 93 * specified multimap. 94 * 95 * @param multimap the multimap whose contents are copied to this multimap 96 */ 97 public static <K, V> ArrayListMultimap<K, V> create( 98 Multimap<? extends K, ? extends V> multimap) { 99 return new ArrayListMultimap<K, V>(multimap); 100 } 101 102 private ArrayListMultimap() { 103 super(new HashMap<K, Collection<V>>()); 104 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 105 } 106 107 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) { 108 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys)); 109 checkArgument(expectedValuesPerKey >= 0); 110 this.expectedValuesPerKey = expectedValuesPerKey; 111 } 112 113 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) { 114 this(multimap.keySet().size(), 115 (multimap instanceof ArrayListMultimap) ? 116 ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey : 117 DEFAULT_VALUES_PER_KEY); 118 putAll(multimap); 119 } 120 121 /** 122 * Creates a new, empty {@code ArrayList} to hold the collection of values for 123 * an arbitrary key. 124 */ 125 @Override List<V> createCollection() { 126 return new ArrayList<V>(expectedValuesPerKey); 127 } 128 129 /** 130 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible. 131 */ 132 public void trimToSize() { 133 for (Collection<V> collection : backingMap().values()) { 134 ArrayList<V> arrayList = (ArrayList<V>) collection; 135 arrayList.trimToSize(); 136 } 137 } 138 139 /** 140 * @serialData expectedValuesPerKey, number of distinct keys, and then for 141 * each distinct key: the key, number of values for that key, and the 142 * key's values 143 */ 144 @GwtIncompatible("java.io.ObjectOutputStream") 145 private void writeObject(ObjectOutputStream stream) throws IOException { 146 stream.defaultWriteObject(); 147 stream.writeInt(expectedValuesPerKey); 148 Serialization.writeMultimap(this, stream); 149 } 150 151 @GwtIncompatible("java.io.ObjectOutputStream") 152 private void readObject(ObjectInputStream stream) 153 throws IOException, ClassNotFoundException { 154 stream.defaultReadObject(); 155 expectedValuesPerKey = stream.readInt(); 156 int distinctKeys = Serialization.readCount(stream); 157 Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys); 158 setMap(map); 159 Serialization.populateMultimap(this, stream, distinctKeys); 160 } 161 162 @GwtIncompatible("Not needed in emulated source.") 163 private static final long serialVersionUID = 0; 164 } 165
