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 com.google.common.annotations.GwtCompatible; 20 import com.google.common.annotations.GwtIncompatible; 21 import com.google.common.annotations.VisibleForTesting; 22 import com.google.common.base.Preconditions; 23 import java.io.IOException; 24 import java.io.ObjectInputStream; 25 import java.io.ObjectOutputStream; 26 import java.util.Collection; 27 import java.util.Map; 28 import java.util.Set; 29 30 /** 31 * Implementation of {@link Multimap} using hash tables. 32 * 33 * <p>The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an 34 * existing key-value pair has no effect. 35 * 36 * <p>Keys and values may be null. All optional multimap methods are supported, and all returned 37 * views are modifiable. 38 * 39 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent 40 * read operations will work correctly if the last write <i>happens-before</i> any reads. To allow 41 * concurrent update operations, wrap your multimap with a call to {@link 42 * Multimaps#synchronizedSetMultimap}. 43 * 44 * @author Jared Levy 45 * @since 2.0 46 */ 47 @GwtCompatible(serializable = true, emulated = true) 48 public final class HashMultimap<K, V> extends HashMultimapGwtSerializationDependencies<K, V> { 49 private static final int DEFAULT_VALUES_PER_KEY = 2; 50 51 @VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 52 53 /** 54 * Creates a new, empty {@code HashMultimap} with the default initial capacities. 55 * 56 * <p>This method will soon be deprecated in favor of {@code 57 * MultimapBuilder.hashKeys().hashSetValues().build()}. 58 */ create()59 public static <K, V> HashMultimap<K, V> create() { 60 return new HashMultimap<>(); 61 } 62 63 /** 64 * Constructs an empty {@code HashMultimap} with enough capacity to hold the specified numbers of 65 * keys and values without rehashing. 66 * 67 * <p>This method will soon be deprecated in favor of {@code 68 * MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build()}. 69 * 70 * @param expectedKeys the expected number of distinct keys 71 * @param expectedValuesPerKey the expected average number of values per key 72 * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is 73 * negative 74 */ create(int expectedKeys, int expectedValuesPerKey)75 public static <K, V> HashMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) { 76 return new HashMultimap<>(expectedKeys, expectedValuesPerKey); 77 } 78 79 /** 80 * Constructs a {@code HashMultimap} with the same mappings as the specified multimap. If a 81 * key-value mapping appears multiple times in the input multimap, it only appears once in the 82 * constructed multimap. 83 * 84 * <p>This method will soon be deprecated in favor of {@code 85 * MultimapBuilder.hashKeys().hashSetValues().build(multimap)}. 86 * 87 * @param multimap the multimap whose contents are copied to this multimap 88 */ create(Multimap<? extends K, ? extends V> multimap)89 public static <K, V> HashMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) { 90 return new HashMultimap<>(multimap); 91 } 92 HashMultimap()93 private HashMultimap() { 94 this(12, DEFAULT_VALUES_PER_KEY); 95 } 96 HashMultimap(int expectedKeys, int expectedValuesPerKey)97 private HashMultimap(int expectedKeys, int expectedValuesPerKey) { 98 super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys)); 99 Preconditions.checkArgument(expectedValuesPerKey >= 0); 100 this.expectedValuesPerKey = expectedValuesPerKey; 101 } 102 HashMultimap(Multimap<? extends K, ? extends V> multimap)103 private HashMultimap(Multimap<? extends K, ? extends V> multimap) { 104 super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(multimap.keySet().size())); 105 putAll(multimap); 106 } 107 108 /** 109 * {@inheritDoc} 110 * 111 * <p>Creates an empty {@code HashSet} for a collection of values for one key. 112 * 113 * @return a new {@code HashSet} containing a collection of values for one key 114 */ 115 @Override createCollection()116 Set<V> createCollection() { 117 return Platform.<V>newHashSetWithExpectedSize(expectedValuesPerKey); 118 } 119 120 /** 121 * @serialData expectedValuesPerKey, number of distinct keys, and then for each distinct key: the 122 * key, number of values for that key, and the key's values 123 */ 124 @GwtIncompatible // java.io.ObjectOutputStream writeObject(ObjectOutputStream stream)125 private void writeObject(ObjectOutputStream stream) throws IOException { 126 stream.defaultWriteObject(); 127 Serialization.writeMultimap(this, stream); 128 } 129 130 @GwtIncompatible // java.io.ObjectInputStream readObject(ObjectInputStream stream)131 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException { 132 stream.defaultReadObject(); 133 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; 134 int distinctKeys = Serialization.readCount(stream); 135 Map<K, Collection<V>> map = Platform.newHashMapWithExpectedSize(12); 136 setMap(map); 137 Serialization.populateMultimap(this, stream, distinctKeys); 138 } 139 140 @GwtIncompatible // Not needed in emulated source 141 private static final long serialVersionUID = 0; 142 } 143