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 * @author Jared Levy
060 * @since 2.0 (imported from Google Collections Library)
061 */
062 @GwtCompatible(serializable = true, emulated = true)
063 public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
064 // Default from ArrayList
065 private static final int DEFAULT_VALUES_PER_KEY = 10;
066
067 @VisibleForTesting transient int expectedValuesPerKey;
068
069 /**
070 * Creates a new, empty {@code ArrayListMultimap} with the default initial
071 * capacities.
072 */
073 public static <K, V> ArrayListMultimap<K, V> create() {
074 return new ArrayListMultimap<K, V>();
075 }
076
077 /**
078 * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold
079 * the specified numbers of keys and values without resizing.
080 *
081 * @param expectedKeys the expected number of distinct keys
082 * @param expectedValuesPerKey the expected average number of values per key
083 * @throws IllegalArgumentException if {@code expectedKeys} or {@code
084 * expectedValuesPerKey} is negative
085 */
086 public static <K, V> ArrayListMultimap<K, V> create(
087 int expectedKeys, int expectedValuesPerKey) {
088 return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
089 }
090
091 /**
092 * Constructs an {@code ArrayListMultimap} with the same mappings as the
093 * specified multimap.
094 *
095 * @param multimap the multimap whose contents are copied to this multimap
096 */
097 public static <K, V> ArrayListMultimap<K, V> create(
098 Multimap<? extends K, ? extends V> multimap) {
099 return new ArrayListMultimap<K, V>(multimap);
100 }
101
102 private ArrayListMultimap() {
103 super(new HashMap<K, Collection<V>>());
104 expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
105 }
106
107 private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
108 super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
109 checkArgument(expectedValuesPerKey >= 0);
110 this.expectedValuesPerKey = expectedValuesPerKey;
111 }
112
113 private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
114 this(multimap.keySet().size(),
115 (multimap instanceof ArrayListMultimap) ?
116 ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey :
117 DEFAULT_VALUES_PER_KEY);
118 putAll(multimap);
119 }
120
121 /**
122 * Creates a new, empty {@code ArrayList} to hold the collection of values for
123 * an arbitrary key.
124 */
125 @Override List<V> createCollection() {
126 return new ArrayList<V>(expectedValuesPerKey);
127 }
128
129 /**
130 * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
131 */
132 public void trimToSize() {
133 for (Collection<V> collection : backingMap().values()) {
134 ArrayList<V> arrayList = (ArrayList<V>) collection;
135 arrayList.trimToSize();
136 }
137 }
138
139 /**
140 * @serialData expectedValuesPerKey, number of distinct keys, and then for
141 * each distinct key: the key, number of values for that key, and the
142 * key's values
143 */
144 @GwtIncompatible("java.io.ObjectOutputStream")
145 private void writeObject(ObjectOutputStream stream) throws IOException {
146 stream.defaultWriteObject();
147 stream.writeInt(expectedValuesPerKey);
148 Serialization.writeMultimap(this, stream);
149 }
150
151 @GwtIncompatible("java.io.ObjectOutputStream")
152 private void readObject(ObjectInputStream stream)
153 throws IOException, ClassNotFoundException {
154 stream.defaultReadObject();
155 expectedValuesPerKey = stream.readInt();
156 int distinctKeys = Serialization.readCount(stream);
157 Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
158 setMap(map);
159 Serialization.populateMultimap(this, stream, distinctKeys);
160 }
161
162 @GwtIncompatible("Not needed in emulated source.")
163 private static final long serialVersionUID = 0;
164 }