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 static com.google.common.base.Preconditions.checkArgument;
020
021 import com.google.common.annotations.GwtCompatible;
022 import com.google.common.annotations.GwtIncompatible;
023 import com.google.common.annotations.VisibleForTesting;
024
025 import java.io.IOException;
026 import java.io.ObjectInputStream;
027 import java.io.ObjectOutputStream;
028 import java.util.ArrayList;
029 import java.util.Collection;
030 import java.util.HashMap;
031 import java.util.List;
032 import java.util.Map;
033
034 /**
035 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store
036 * the values for a given key. A {@link HashMap} associates each key with an
037 * {@link ArrayList} of values.
038 *
039 * <p>When iterating through the collections supplied by this class, the
040 * ordering of values for a given key agrees with the order in which the values
041 * were added.
042 *
043 * <p>This multimap allows duplicate key-value pairs. After adding a new
044 * key-value pair equal to an existing key-value pair, the {@code
045 * ArrayListMultimap} will contain entries for both the new value and the old
046 * value.
047 *
048 * <p>Keys and values may be null. All optional multimap methods are supported,
049 * and all returned views are modifiable.
050 *
051 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link
052 * #replaceValues} all implement {@link java.util.RandomAccess}.
053 *
054 * <p>This class is not threadsafe when any concurrent operations update the
055 * multimap. Concurrent read operations will work correctly. To allow concurrent
056 * update operations, wrap your multimap with a call to {@link
057 * Multimaps#synchronizedListMultimap}.
058 *
059 * <p>See the Guava User Guide article on <a href=
060 * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap">
061 * {@code Multimap}</a>.
062 *
063 * @author Jared Levy
064 * @since 2.0 (imported from Google Collections Library)
065 */
066 @GwtCompatible(serializable = true, emulated = true)
067 public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
068 // Default from ArrayList
069 private static final int DEFAULT_VALUES_PER_KEY = 3;
070
071 @VisibleForTesting transient int expectedValuesPerKey;
072
073 /**
074 * Creates a new, empty {@code ArrayListMultimap} with the default initial
075 * capacities.
076 */
077 public static <K, V> ArrayListMultimap<K, V> create() {
078 return new ArrayListMultimap<K, V>();
079 }
080
081 /**
082 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold
083 * the specified numbers of keys and values without resizing.
084 *
085 * @param expectedKeys the expected number of distinct keys
086 * @param expectedValuesPerKey the expected average number of values per key
087 * @throws IllegalArgumentException if {@code expectedKeys} or {@code
088 * expectedValuesPerKey} is negative
089 */
090 public static <K, V> ArrayListMultimap<K, V> create(
091 int expectedKeys, int expectedValuesPerKey) {
092 return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
093 }
094
095 /**
096 * Constructs an {@code ArrayListMultimap} with the same mappings as the
097 * specified multimap.
098 *
099 * @param multimap the multimap whose contents are copied to this multimap
100 */
101 public static <K, V> ArrayListMultimap<K, V> create(
102 Multimap<? extends K, ? extends V> multimap) {
103 return new ArrayListMultimap<K, V>(multimap);
104 }
105
106 private ArrayListMultimap() {
107 super(new HashMap<K, Collection<V>>());
108 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
109 }
110
111 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
112 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
113 checkArgument(expectedValuesPerKey >= 0);
114 this.expectedValuesPerKey = expectedValuesPerKey;
115 }
116
117 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
118 this(multimap.keySet().size(),
119 (multimap instanceof ArrayListMultimap) ?
120 ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey :
121 DEFAULT_VALUES_PER_KEY);
122 putAll(multimap);
123 }
124
125 /**
126 * Creates a new, empty {@code ArrayList} to hold the collection of values for
127 * an arbitrary key.
128 */
129 @Override List<V> createCollection() {
130 return new ArrayList<V>(expectedValuesPerKey);
131 }
132
133 /**
134 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
135 */
136 public void trimToSize() {
137 for (Collection<V> collection : backingMap().values()) {
138 ArrayList<V> arrayList = (ArrayList<V>) collection;
139 arrayList.trimToSize();
140 }
141 }
142
143 /**
144 * @serialData expectedValuesPerKey, number of distinct keys, and then for
145 * each distinct key: the key, number of values for that key, and the
146 * key's values
147 */
148 @GwtIncompatible("java.io.ObjectOutputStream")
149 private void writeObject(ObjectOutputStream stream) throws IOException {
150 stream.defaultWriteObject();
151 stream.writeInt(expectedValuesPerKey);
152 Serialization.writeMultimap(this, stream);
153 }
154
155 @GwtIncompatible("java.io.ObjectOutputStream")
156 private void readObject(ObjectInputStream stream)
157 throws IOException, ClassNotFoundException {
158 stream.defaultReadObject();
159 expectedValuesPerKey = stream.readInt();
160 int distinctKeys = Serialization.readCount(stream);
161 Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
162 setMap(map);
163 Serialization.populateMultimap(this, stream, distinctKeys);
164 }
165
166 @GwtIncompatible("Not needed in emulated source.")
167 private static final long serialVersionUID = 0;
168 }