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.base.Preconditions.checkArgument;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.VisibleForTesting;
024
025import java.io.IOException;
026import java.io.ObjectInputStream;
027import java.io.ObjectOutputStream;
028import java.util.ArrayList;
029import java.util.Collection;
030import java.util.HashMap;
031import java.util.List;
032import 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 (imported from Google Collections Library)
061 */
062@GwtCompatible(serializable = true, emulated = true)
063public 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}