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.VisibleForTesting;
21 import com.google.common.base.Preconditions;
22
23 import java.util.Collection;
24 import java.util.HashMap;
25 import 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)
45 public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
46 private static final int DEFAULT_VALUES_PER_KEY = 2;
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