1/*
2 * Copyright (C) 2007 Google Inc.
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 com.google.common.annotations.GwtCompatible;
20import com.google.common.annotations.VisibleForTesting;
21import com.google.common.base.Preconditions;
22
23import java.io.IOException;
24import java.io.ObjectInputStream;
25import java.io.ObjectOutputStream;
26import java.util.Collection;
27import java.util.HashMap;
28import java.util.Map;
29import java.util.Set;
30
31/**
32 * Implementation of {@link Multimap} using hash tables.
33 *
34 * <p>The multimap does not store duplicate key-value pairs. Adding a new
35 * key-value pair equal to an existing key-value pair has no effect.
36 *
37 * <p>Keys and values may be null. All optional multimap methods are supported,
38 * and all returned views are modifiable.
39 *
40 * <p>This class is not threadsafe when any concurrent operations update the
41 * multimap. Concurrent read operations will work correctly. To allow concurrent
42 * update operations, wrap your multimap with a call to {@link
43 * Multimaps#synchronizedSetMultimap}.
44 *
45 * @author Jared Levy
46 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
47 */
48@GwtCompatible(serializable = true)
49public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
50  private static final int DEFAULT_VALUES_PER_KEY = 8;
51
52  @VisibleForTesting
53  transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
54
55  /**
56   * Creates a new, empty {@code HashMultimap} with the default initial
57   * capacities.
58   */
59  public static <K, V> HashMultimap<K, V> create() {
60    return new HashMultimap<K, V>();
61  }
62
63  /**
64   * Constructs an empty {@code HashMultimap} with enough capacity to hold the
65   * specified numbers of keys and values without rehashing.
66   *
67   * @param expectedKeys the expected number of distinct keys
68   * @param expectedValuesPerKey the expected average number of values per key
69   * @throws IllegalArgumentException if {@code expectedKeys} or {@code
70   *      expectedValuesPerKey} is negative
71   */
72  public static <K, V> HashMultimap<K, V> create(
73      int expectedKeys, int expectedValuesPerKey) {
74    return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
75  }
76
77  /**
78   * Constructs a {@code HashMultimap} with the same mappings as the specified
79   * multimap. If a key-value mapping appears multiple times in the input
80   * multimap, it only appears once in the constructed multimap.
81   *
82   * @param multimap the multimap whose contents are copied to this multimap
83   */
84  public static <K, V> HashMultimap<K, V> create(
85      Multimap<? extends K, ? extends V> multimap) {
86    return new HashMultimap<K, V>(multimap);
87  }
88
89  private HashMultimap() {
90    super(new HashMap<K, Collection<V>>());
91  }
92
93  private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
94    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
95    Preconditions.checkArgument(expectedValuesPerKey >= 0);
96    this.expectedValuesPerKey = expectedValuesPerKey;
97  }
98
99  private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
100    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(
101        multimap.keySet().size()));
102    putAll(multimap);
103  }
104
105  /**
106   * {@inheritDoc}
107   *
108   * <p>Creates an empty {@code HashSet} for a collection of values for one key.
109   *
110   * @return a new {@code HashSet} containing a collection of values for one key
111   */
112  @Override Set<V> createCollection() {
113    return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
114  }
115
116  /**
117   * @serialData expectedValuesPerKey, number of distinct keys, and then for
118   *     each distinct key: the key, number of values for that key, and the
119   *     key's values
120   */
121  private void writeObject(ObjectOutputStream stream) throws IOException {
122    stream.defaultWriteObject();
123    stream.writeInt(expectedValuesPerKey);
124    Serialization.writeMultimap(this, stream);
125  }
126
127  private void readObject(ObjectInputStream stream)
128      throws IOException, ClassNotFoundException {
129    stream.defaultReadObject();
130    expectedValuesPerKey = stream.readInt();
131    int distinctKeys = Serialization.readCount(stream);
132    Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
133    setMap(map);
134    Serialization.populateMultimap(this, stream, distinctKeys);
135  }
136
137  private static final long serialVersionUID = 0;
138}
139