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;
032
033/**
034 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store
035 * the values for a given key. A {@link HashMap} associates each key with an
036 * {@link ArrayList} of values.
037 *
038 * <p>When iterating through the collections supplied by this class, the
039 * ordering of values for a given key agrees with the order in which the values
040 * were added.
041 *
042 * <p>This multimap allows duplicate key-value pairs. After adding a new
043 * key-value pair equal to an existing key-value pair, the {@code
044 * ArrayListMultimap} will contain entries for both the new value and the old
045 * value.
046 *
047 * <p>Keys and values may be null. All optional multimap methods are supported,
048 * and all returned views are modifiable.
049 *
050 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link
051 * #replaceValues} all implement {@link java.util.RandomAccess}.
052 *
053 * <p>This class is not threadsafe when any concurrent operations update the
054 * multimap. Concurrent read operations will work correctly. To allow concurrent
055 * update operations, wrap your multimap with a call to {@link
056 * Multimaps#synchronizedListMultimap}.
057 *
058 * <p>See the Guava User Guide article on <a href=
059 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap">
060 * {@code Multimap}</a>.
061 *
062 * @author Jared Levy
063 * @since 2.0
064 */
065@GwtCompatible(serializable = true, emulated = true)
066public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
067  // Default from ArrayList
068  private static final int DEFAULT_VALUES_PER_KEY = 3;
069
070  @VisibleForTesting transient int expectedValuesPerKey;
071
072  /**
073   * Creates a new, empty {@code ArrayListMultimap} with the default initial capacities.
074   *
075   * <p>This method will soon be deprecated in favor of {@code
076   * MultimapBuilder.hashKeys().arrayListValues().build()}.
077   */
078  public static <K, V> ArrayListMultimap<K, V> create() {
079    return new ArrayListMultimap<K, V>();
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, V> ArrayListMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
095    return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
096  }
097
098  /**
099   * Constructs an {@code ArrayListMultimap} with the same mappings as the specified multimap.
100   *
101   * <p>This method will soon be deprecated in favor of {@code
102   * MultimapBuilder.hashKeys().arrayListValues().build(multimap)}.
103   *
104   * @param multimap the multimap whose contents are copied to this multimap
105   */
106  public static <K, V> ArrayListMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
107    return new ArrayListMultimap<K, V>(multimap);
108  }
109
110  private ArrayListMultimap() {
111    super(new HashMap<K, Collection<V>>());
112    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
113  }
114
115  private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
116    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
117    checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey");
118    this.expectedValuesPerKey = expectedValuesPerKey;
119  }
120
121  private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
122    this(
123        multimap.keySet().size(),
124        (multimap instanceof ArrayListMultimap)
125            ? ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey
126            : DEFAULT_VALUES_PER_KEY);
127    putAll(multimap);
128  }
129
130  /**
131   * Creates a new, empty {@code ArrayList} to hold the collection of values for
132   * 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>>}. This method is scheduled for removal
145   *     in April 2019.
146   */
147  @Deprecated
148  public void trimToSize() {
149    for (Collection<V> collection : backingMap().values()) {
150      ArrayList<V> arrayList = (ArrayList<V>) collection;
151      arrayList.trimToSize();
152    }
153  }
154
155  /**
156   * @serialData expectedValuesPerKey, number of distinct keys, and then for
157   *     each distinct key: the key, number of values for that key, and the
158   *     key's values
159   */
160  @GwtIncompatible // java.io.ObjectOutputStream
161  private void writeObject(ObjectOutputStream stream) throws IOException {
162    stream.defaultWriteObject();
163    Serialization.writeMultimap(this, stream);
164  }
165
166  @GwtIncompatible // java.io.ObjectOutputStream
167  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
168    stream.defaultReadObject();
169    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
170    int distinctKeys = Serialization.readCount(stream);
171    Map<K, Collection<V>> map = Maps.newHashMap();
172    setMap(map);
173    Serialization.populateMultimap(this, stream, distinctKeys);
174  }
175
176  @GwtIncompatible // Not needed in emulated source.
177  private static final long serialVersionUID = 0;
178}