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 com.google.common.annotations.GwtCompatible;
20import com.google.common.annotations.VisibleForTesting;
21import com.google.common.base.Preconditions;
22
23import java.util.Collection;
24import java.util.HashMap;
25import java.util.Set;
26
27/**
28 * Implementation of {@link Multimap} using hash tables.
29 *
30 * <p>The multimap does not store duplicate key-value pairs. Adding a new
31 * key-value pair equal to an existing key-value pair has no effect.
32 *
33 * <p>Keys and values may be null. All optional multimap methods are supported,
34 * and all returned views are modifiable.
35 *
36 * <p>This class is not threadsafe when any concurrent operations update the
37 * multimap. Concurrent read operations will work correctly. To allow concurrent
38 * update operations, wrap your multimap with a call to {@link
39 * Multimaps#synchronizedSetMultimap}.
40 *
41 * @author Jared Levy
42 * @since 2.0 (imported from Google Collections Library)
43 */
44@GwtCompatible(serializable = true, emulated = true)
45public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
46  private static final int DEFAULT_VALUES_PER_KEY = 8;
47
48  @VisibleForTesting
49  transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
50
51  /**
52   * Creates a new, empty {@code HashMultimap} with the default initial
53   * capacities.
54   */
55  public static <K, V> HashMultimap<K, V> create() {
56    return new HashMultimap<K, V>();
57  }
58
59  /**
60   * Constructs an empty {@code HashMultimap} with enough capacity to hold the
61   * specified numbers of keys and values without rehashing.
62   *
63   * @param expectedKeys the expected number of distinct keys
64   * @param expectedValuesPerKey the expected average number of values per key
65   * @throws IllegalArgumentException if {@code expectedKeys} or {@code
66   *      expectedValuesPerKey} is negative
67   */
68  public static <K, V> HashMultimap<K, V> create(
69      int expectedKeys, int expectedValuesPerKey) {
70    return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
71  }
72
73  /**
74   * Constructs a {@code HashMultimap} with the same mappings as the specified
75   * multimap. If a key-value mapping appears multiple times in the input
76   * multimap, it only appears once in the constructed multimap.
77   *
78   * @param multimap the multimap whose contents are copied to this multimap
79   */
80  public static <K, V> HashMultimap<K, V> create(
81      Multimap<? extends K, ? extends V> multimap) {
82    return new HashMultimap<K, V>(multimap);
83  }
84
85  private HashMultimap() {
86    super(new HashMap<K, Collection<V>>());
87  }
88
89  private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
90    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
91    Preconditions.checkArgument(expectedValuesPerKey >= 0);
92    this.expectedValuesPerKey = expectedValuesPerKey;
93  }
94
95  private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
96    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(
97        multimap.keySet().size()));
98    putAll(multimap);
99  }
100
101  /**
102   * {@inheritDoc}
103   *
104   * <p>Creates an empty {@code HashSet} for a collection of values for one key.
105   *
106   * @return a new {@code HashSet} containing a collection of values for one key
107   */
108  @Override Set<V> createCollection() {
109    return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
110  }
111}
112
113