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
017package com.google.common.collect;
018
019import static com.google.common.collect.CollectPreconditions.checkNonnegative;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.VisibleForTesting;
024import java.io.IOException;
025import java.io.ObjectInputStream;
026import java.io.ObjectOutputStream;
027import java.util.ArrayList;
028import java.util.Collection;
029import java.util.HashMap;
030import java.util.List;
031import java.util.Map;
032import org.checkerframework.checker.nullness.qual.Nullable;
033
034/**
035 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store the values for a given
036 * key. A {@link HashMap} associates each key with an {@link ArrayList} of values.
037 *
038 * <p>When iterating through the collections supplied by this class, the ordering of values for a
039 * given key agrees with the order in which the values were added.
040 *
041 * <p>This multimap allows duplicate key-value pairs. After adding a new key-value pair equal to an
042 * existing key-value pair, the {@code ArrayListMultimap} will contain entries for both the new
043 * value and the old value.
044 *
045 * <p>Keys and values may be null. All optional multimap methods are supported, and all returned
046 * views are modifiable.
047 *
048 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link #replaceValues} all
049 * implement {@link java.util.RandomAccess}.
050 *
051 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
052 * read operations will work correctly. To allow concurrent update operations, wrap your multimap
053 * with a call to {@link Multimaps#synchronizedListMultimap}.
054 *
055 * <p>See the Guava User Guide article on <a href=
056 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> {@code
057 * Multimap}</a>.
058 *
059 * @author Jared Levy
060 * @since 2.0
061 */
062@GwtCompatible(serializable = true, emulated = true)
063@ElementTypesAreNonnullByDefault
064public final class ArrayListMultimap<K extends @Nullable Object, V extends @Nullable Object>
065    extends ArrayListMultimapGwtSerializationDependencies<K, V> {
066  // Default from ArrayList
067  private static final int DEFAULT_VALUES_PER_KEY = 3;
068
069  @VisibleForTesting transient int expectedValuesPerKey;
070
071  /**
072   * Creates a new, empty {@code ArrayListMultimap} with the default initial capacities.
073   *
074   * <p>This method will soon be deprecated in favor of {@code
075   * MultimapBuilder.hashKeys().arrayListValues().build()}.
076   */
077  public static <K extends @Nullable Object, V extends @Nullable Object>
078      ArrayListMultimap<K, V> create() {
079    return new ArrayListMultimap<>();
080  }
081
082  /**
083   * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold the specified
084   * numbers of keys and values without resizing.
085   *
086   * <p>This method will soon be deprecated in favor of {@code
087   * MultimapBuilder.hashKeys(expectedKeys).arrayListValues(expectedValuesPerKey).build()}.
088   *
089   * @param expectedKeys the expected number of distinct keys
090   * @param expectedValuesPerKey the expected average number of values per key
091   * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
092   *     negative
093   */
094  public static <K extends @Nullable Object, V extends @Nullable Object>
095      ArrayListMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
096    return new ArrayListMultimap<>(expectedKeys, expectedValuesPerKey);
097  }
098
099  /**
100   * Constructs an {@code ArrayListMultimap} with the same mappings as the specified multimap.
101   *
102   * <p>This method will soon be deprecated in favor of {@code
103   * MultimapBuilder.hashKeys().arrayListValues().build(multimap)}.
104   *
105   * @param multimap the multimap whose contents are copied to this multimap
106   */
107  public static <K extends @Nullable Object, V extends @Nullable Object>
108      ArrayListMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
109    return new ArrayListMultimap<>(multimap);
110  }
111
112  private ArrayListMultimap() {
113    this(12, DEFAULT_VALUES_PER_KEY);
114  }
115
116  private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
117    super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
118    checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey");
119    this.expectedValuesPerKey = expectedValuesPerKey;
120  }
121
122  private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
123    this(
124        multimap.keySet().size(),
125        (multimap instanceof ArrayListMultimap)
126            ? ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey
127            : DEFAULT_VALUES_PER_KEY);
128    putAll(multimap);
129  }
130
131  /**
132   * Creates a new, empty {@code ArrayList} to hold the collection of values for an arbitrary key.
133   */
134  @Override
135  List<V> createCollection() {
136    return new ArrayList<V>(expectedValuesPerKey);
137  }
138
139  /**
140   * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
141   *
142   * @deprecated For a {@link ListMultimap} that automatically trims to size, use {@link
143   *     ImmutableListMultimap}. If you need a mutable collection, remove the {@code trimToSize}
144   *     call, or switch to a {@code HashMap<K, ArrayList<V>>}.
145   */
146  @Deprecated
147  public void trimToSize() {
148    for (Collection<V> collection : backingMap().values()) {
149      ArrayList<V> arrayList = (ArrayList<V>) collection;
150      arrayList.trimToSize();
151    }
152  }
153
154  /**
155   * @serialData expectedValuesPerKey, number of distinct keys, and then for each distinct key: the
156   *     key, number of values for that key, and the key's values
157   */
158  @GwtIncompatible // java.io.ObjectOutputStream
159  private void writeObject(ObjectOutputStream stream) throws IOException {
160    stream.defaultWriteObject();
161    Serialization.writeMultimap(this, stream);
162  }
163
164  @GwtIncompatible // java.io.ObjectOutputStream
165  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
166    stream.defaultReadObject();
167    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
168    int distinctKeys = Serialization.readCount(stream);
169    Map<K, Collection<V>> map = CompactHashMap.create();
170    setMap(map);
171    Serialization.populateMultimap(this, stream, distinctKeys);
172  }
173
174  @GwtIncompatible // Not needed in emulated source.
175  private static final long serialVersionUID = 0;
176}