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 com.google.common.annotations.GwtCompatible;
020import com.google.common.annotations.GwtIncompatible;
021import com.google.common.annotations.VisibleForTesting;
022import com.google.common.base.Preconditions;
023import java.io.IOException;
024import java.io.ObjectInputStream;
025import java.io.ObjectOutputStream;
026import java.util.Collection;
027import java.util.HashMap;
028import java.util.Map;
029import java.util.Set;
030
031/**
032 * Implementation of {@link Multimap} using hash tables.
033 *
034 * <p>The multimap does not store duplicate key-value pairs. Adding a new
035 * key-value pair equal to an existing key-value pair has no effect.
036 *
037 * <p>Keys and values may be null. All optional multimap methods are supported,
038 * and all returned views are modifiable.
039 *
040 * <p>This class is not threadsafe when any concurrent operations update the
041 * multimap. Concurrent read operations will work correctly. To allow concurrent
042 * update operations, wrap your multimap with a call to {@link
043 * Multimaps#synchronizedSetMultimap}.
044 *
045 * @author Jared Levy
046 * @since 2.0
047 */
048@GwtCompatible(serializable = true, emulated = true)
049public final class HashMultimap<K, V> extends HashMultimapGwtSerializationDependencies<K, V> {
050  private static final int DEFAULT_VALUES_PER_KEY = 2;
051
052  @VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
053
054  /**
055   * Creates a new, empty {@code HashMultimap} with the default initial capacities.
056   *
057   * <p>This method will soon be deprecated in favor of {@code
058   * MultimapBuilder.hashKeys().hashSetValues().build()}.
059   */
060  public static <K, V> HashMultimap<K, V> create() {
061    return new HashMultimap<K, V>();
062  }
063
064  /**
065   * Constructs an empty {@code HashMultimap} with enough capacity to hold the specified numbers of
066   * keys and values without rehashing.
067   *
068   * <p>This method will soon be deprecated in favor of {@code
069   * MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build()}.
070   *
071   * @param expectedKeys the expected number of distinct keys
072   * @param expectedValuesPerKey the expected average number of values per key
073   * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
074   *     negative
075   */
076  public static <K, V> HashMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
077    return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
078  }
079
080  /**
081   * Constructs a {@code HashMultimap} with the same mappings as the specified multimap. If a
082   * key-value mapping appears multiple times in the input multimap, it only appears once in the
083   * constructed multimap.
084   *
085   * <p>This method will soon be deprecated in favor of {@code
086   * MultimapBuilder.hashKeys().hashSetValues().build(multimap)}.
087   *
088   * @param multimap the multimap whose contents are copied to this multimap
089   */
090  public static <K, V> HashMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
091    return new HashMultimap<K, V>(multimap);
092  }
093
094  private HashMultimap() {
095    super(new HashMap<K, Collection<V>>());
096  }
097
098  private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
099    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
100    Preconditions.checkArgument(expectedValuesPerKey >= 0);
101    this.expectedValuesPerKey = expectedValuesPerKey;
102  }
103
104  private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
105    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(multimap.keySet().size()));
106    putAll(multimap);
107  }
108
109  /**
110   * {@inheritDoc}
111   *
112   * <p>Creates an empty {@code HashSet} for a collection of values for one key.
113   *
114   * @return a new {@code HashSet} containing a collection of values for one key
115   */
116  @Override
117  Set<V> createCollection() {
118    return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
119  }
120
121  /**
122   * @serialData expectedValuesPerKey, number of distinct keys, and then for
123   *     each distinct key: the key, number of values for that key, and the
124   *     key's values
125   */
126  @GwtIncompatible // java.io.ObjectOutputStream
127  private void writeObject(ObjectOutputStream stream) throws IOException {
128    stream.defaultWriteObject();
129    Serialization.writeMultimap(this, stream);
130  }
131
132  @GwtIncompatible // java.io.ObjectInputStream
133  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
134    stream.defaultReadObject();
135    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
136    int distinctKeys = Serialization.readCount(stream);
137    Map<K, Collection<V>> map = Maps.newHashMap();
138    setMap(map);
139    Serialization.populateMultimap(this, stream, distinctKeys);
140  }
141
142  @GwtIncompatible // Not needed in emulated source
143  private static final long serialVersionUID = 0;
144}