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 static com.google.common.collect.CollectPreconditions.checkNonnegative;
20
21 import com.google.common.annotations.GwtCompatible;
22 import com.google.common.annotations.GwtIncompatible;
23 import com.google.common.annotations.VisibleForTesting;
24 import java.io.IOException;
25 import java.io.ObjectInputStream;
26 import java.io.ObjectOutputStream;
27 import java.util.ArrayList;
28 import java.util.Collection;
29 import java.util.HashMap;
30 import java.util.List;
31 import java.util.Map;
32
33 /**
34 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store the values for a given
35 * key. A {@link HashMap} associates each key with an {@link ArrayList} of values.
36 *
37 * <p>When iterating through the collections supplied by this class, the ordering of values for a
38 * given key agrees with the order in which the values were added.
39 *
40 * <p>This multimap allows duplicate key-value pairs. After adding a new key-value pair equal to an
41 * existing key-value pair, the {@code ArrayListMultimap} will contain entries for both the new
42 * value and the old value.
43 *
44 * <p>Keys and values may be null. All optional multimap methods are supported, and all returned
45 * views are modifiable.
46 *
47 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link #replaceValues} all
48 * implement {@link java.util.RandomAccess}.
49 *
50 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
51 * read operations will work correctly. To allow concurrent update operations, wrap your multimap
52 * with a call to {@link Multimaps#synchronizedListMultimap}.
53 *
54 * <p>See the Guava User Guide article on <a href=
55 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> {@code
56 * Multimap}</a>.
57 *
58 * @author Jared Levy
59 * @since 2.0
60 */
61 @GwtCompatible(serializable = true, emulated = true)
62 public final class ArrayListMultimap<K, V>
63 extends ArrayListMultimapGwtSerializationDependencies<K, V> {
64 // Default from ArrayList
65 private static final int DEFAULT_VALUES_PER_KEY = 3;
66
67 @VisibleForTesting transient int expectedValuesPerKey;
68
69 /**
70 * Creates a new, empty {@code ArrayListMultimap} with the default initial capacities.
71 *
72 * <p>This method will soon be deprecated in favor of {@code
73 * MultimapBuilder.hashKeys().arrayListValues().build()}.
74 */
75 public static <K, V> ArrayListMultimap<K, V> create() {
76 return new ArrayListMultimap<>();
77 }
78
79 /**
80 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold the specified
81 * numbers of keys and values without resizing.
82 *
83 * <p>This method will soon be deprecated in favor of {@code
84 * MultimapBuilder.hashKeys(expectedKeys).arrayListValues(expectedValuesPerKey).build()}.
85 *
86 * @param expectedKeys the expected number of distinct keys
87 * @param expectedValuesPerKey the expected average number of values per key
88 * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
89 * negative
90 */
91 public static <K, V> ArrayListMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
92 return new ArrayListMultimap<>(expectedKeys, expectedValuesPerKey);
93 }
94
95 /**
96 * Constructs an {@code ArrayListMultimap} with the same mappings as the specified multimap.
97 *
98 * <p>This method will soon be deprecated in favor of {@code
99 * MultimapBuilder.hashKeys().arrayListValues().build(multimap)}.
100 *
101 * @param multimap the multimap whose contents are copied to this multimap
102 */
103 public static <K, V> ArrayListMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
104 return new ArrayListMultimap<>(multimap);
105 }
106
107 private ArrayListMultimap() {
108 this(12, DEFAULT_VALUES_PER_KEY);
109 }
110
111 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
112 super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
113 checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey");
114 this.expectedValuesPerKey = expectedValuesPerKey;
115 }
116
117 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
118 this(
119 multimap.keySet().size(),
120 (multimap instanceof ArrayListMultimap)
121 ? ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey
122 : DEFAULT_VALUES_PER_KEY);
123 putAll(multimap);
124 }
125
126 /**
127 * Creates a new, empty {@code ArrayList} to hold the collection of values for an arbitrary key.
128 */
129 @Override
130 List<V> createCollection() {
131 return new ArrayList<V>(expectedValuesPerKey);
132 }
133
134 /**
135 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
136 *
137 * @deprecated For a {@link ListMultimap} that automatically trims to size, use {@link
138 * ImmutableListMultimap}. If you need a mutable collection, remove the {@code trimToSize}
139 * call, or switch to a {@code HashMap<K, ArrayList<V>>}.
140 */
141 @Deprecated
142 public void trimToSize() {
143 for (Collection<V> collection : backingMap().values()) {
144 ArrayList<V> arrayList = (ArrayList<V>) collection;
145 arrayList.trimToSize();
146 }
147 }
148
149 /**
150 * @serialData expectedValuesPerKey, number of distinct keys, and then for each distinct key: the
151 * key, number of values for that key, and the key's values
152 */
153 @GwtIncompatible // java.io.ObjectOutputStream
154 private void writeObject(ObjectOutputStream stream) throws IOException {
155 stream.defaultWriteObject();
156 Serialization.writeMultimap(this, stream);
157 }
158
159 @GwtIncompatible // java.io.ObjectOutputStream
160 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
161 stream.defaultReadObject();
162 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
163 int distinctKeys = Serialization.readCount(stream);
164 Map<K, Collection<V>> map = Maps.newHashMap();
165 setMap(map);
166 Serialization.populateMultimap(this, stream, distinctKeys);
167 }
168
169 @GwtIncompatible // Not needed in emulated source.
170 private static final long serialVersionUID = 0;
171 }