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
017 package com.google.common.collect;
018
019 import com.google.common.annotations.GwtCompatible;
020 import com.google.common.annotations.GwtIncompatible;
021 import com.google.common.annotations.VisibleForTesting;
022 import com.google.common.base.Preconditions;
023
024 import java.io.IOException;
025 import java.io.ObjectInputStream;
026 import java.io.ObjectOutputStream;
027 import java.util.Collection;
028 import java.util.HashMap;
029 import java.util.Map;
030 import java.util.Set;
031
032 /**
033 * Implementation of {@link Multimap} using hash tables.
034 *
035 * <p>The multimap does not store duplicate key-value pairs. Adding a new
036 * key-value pair equal to an existing key-value pair has no effect.
037 *
038 * <p>Keys and values may be null. All optional multimap methods are supported,
039 * and all returned views are modifiable.
040 *
041 * <p>This class is not threadsafe when any concurrent operations update the
042 * multimap. Concurrent read operations will work correctly. To allow concurrent
043 * update operations, wrap your multimap with a call to {@link
044 * Multimaps#synchronizedSetMultimap}.
045 *
046 * @author Jared Levy
047 * @since 2.0 (imported from Google Collections Library)
048 */
049 @GwtCompatible(serializable = true, emulated = true)
050 public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
051 private static final int DEFAULT_VALUES_PER_KEY = 2;
052
053 @VisibleForTesting
054 transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
055
056 /**
057 * Creates a new, empty {@code HashMultimap} with the default initial
058 * capacities.
059 */
060 public static <K, V> HashMultimap<K, V> create() {
061 return new HashMultimap<K, V>();
062 }
063
064 /**
065 * Constructs an empty {@code HashMultimap} with enough capacity to hold the
066 * specified numbers of keys and values without rehashing.
067 *
068 * @param expectedKeys the expected number of distinct keys
069 * @param expectedValuesPerKey the expected average number of values per key
070 * @throws IllegalArgumentException if {@code expectedKeys} or {@code
071 * expectedValuesPerKey} is negative
072 */
073 public static <K, V> HashMultimap<K, V> create(
074 int expectedKeys, int expectedValuesPerKey) {
075 return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
076 }
077
078 /**
079 * Constructs a {@code HashMultimap} with the same mappings as the specified
080 * multimap. If a key-value mapping appears multiple times in the input
081 * multimap, it only appears once in the constructed multimap.
082 *
083 * @param multimap the multimap whose contents are copied to this multimap
084 */
085 public static <K, V> HashMultimap<K, V> create(
086 Multimap<? extends K, ? extends V> multimap) {
087 return new HashMultimap<K, V>(multimap);
088 }
089
090 private HashMultimap() {
091 super(new HashMap<K, Collection<V>>());
092 }
093
094 private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
095 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
096 Preconditions.checkArgument(expectedValuesPerKey >= 0);
097 this.expectedValuesPerKey = expectedValuesPerKey;
098 }
099
100 private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
101 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(
102 multimap.keySet().size()));
103 putAll(multimap);
104 }
105
106 /**
107 * {@inheritDoc}
108 *
109 * <p>Creates an empty {@code HashSet} for a collection of values for one key.
110 *
111 * @return a new {@code HashSet} containing a collection of values for one key
112 */
113 @Override Set<V> createCollection() {
114 return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
115 }
116
117 /**
118 * @serialData expectedValuesPerKey, number of distinct keys, and then for
119 * each distinct key: the key, number of values for that key, and the
120 * key's values
121 */
122 @GwtIncompatible("java.io.ObjectOutputStream")
123 private void writeObject(ObjectOutputStream stream) throws IOException {
124 stream.defaultWriteObject();
125 stream.writeInt(expectedValuesPerKey);
126 Serialization.writeMultimap(this, stream);
127 }
128
129 @GwtIncompatible("java.io.ObjectInputStream")
130 private void readObject(ObjectInputStream stream)
131 throws IOException, ClassNotFoundException {
132 stream.defaultReadObject();
133 expectedValuesPerKey = stream.readInt();
134 int distinctKeys = Serialization.readCount(stream);
135 Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
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 }