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