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.Map;
028import java.util.Set;
029import org.checkerframework.checker.nullness.qual.Nullable;
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 key-value pair equal to an
035 * existing key-value pair has no effect.
036 *
037 * <p>Keys and values may be null. All optional multimap methods are supported, and all returned
038 * views are modifiable.
039 *
040 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
041 * read operations will work correctly if the last write <i>happens-before</i> any reads. To allow
042 * concurrent update operations, wrap your multimap with a call to {@link
043 * Multimaps#synchronizedSetMultimap}.
044 *
045 * <p><b>Warning:</b> Do not modify either a key <i>or a value</i> of a {@code HashMultimap} in a
046 * way that affects its {@link Object#equals} behavior. Undefined behavior and bugs will result.
047 *
048 * @author Jared Levy
049 * @since 2.0
050 */
051@GwtCompatible(serializable = true, emulated = true)
052@ElementTypesAreNonnullByDefault
053public final class HashMultimap<K extends @Nullable Object, V extends @Nullable Object>
054    extends HashMultimapGwtSerializationDependencies<K, V> {
055  private static final int DEFAULT_VALUES_PER_KEY = 2;
056
057  @VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
058
059  /**
060   * Creates a new, empty {@code HashMultimap} with the default initial capacities.
061   *
062   * <p>This method will soon be deprecated in favor of {@code
063   * MultimapBuilder.hashKeys().hashSetValues().build()}.
064   */
065  public static <K extends @Nullable Object, V extends @Nullable Object>
066      HashMultimap<K, V> create() {
067    return new HashMultimap<>();
068  }
069
070  /**
071   * Constructs an empty {@code HashMultimap} with enough capacity to hold the specified numbers of
072   * keys and values without rehashing.
073   *
074   * <p>This method will soon be deprecated in favor of {@code
075   * MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build()}.
076   *
077   * @param expectedKeys the expected number of distinct keys
078   * @param expectedValuesPerKey the expected average number of values per key
079   * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
080   *     negative
081   */
082  public static <K extends @Nullable Object, V extends @Nullable Object> HashMultimap<K, V> create(
083      int expectedKeys, int expectedValuesPerKey) {
084    return new HashMultimap<>(expectedKeys, expectedValuesPerKey);
085  }
086
087  /**
088   * Constructs a {@code HashMultimap} with the same mappings as the specified multimap. If a
089   * key-value mapping appears multiple times in the input multimap, it only appears once in the
090   * constructed multimap.
091   *
092   * <p>This method will soon be deprecated in favor of {@code
093   * MultimapBuilder.hashKeys().hashSetValues().build(multimap)}.
094   *
095   * @param multimap the multimap whose contents are copied to this multimap
096   */
097  public static <K extends @Nullable Object, V extends @Nullable Object> HashMultimap<K, V> create(
098      Multimap<? extends K, ? extends V> multimap) {
099    return new HashMultimap<>(multimap);
100  }
101
102  private HashMultimap() {
103    this(12, DEFAULT_VALUES_PER_KEY);
104  }
105
106  private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
107    super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
108    Preconditions.checkArgument(expectedValuesPerKey >= 0);
109    this.expectedValuesPerKey = expectedValuesPerKey;
110  }
111
112  private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
113    super(Platform.<K, Collection<V>>newHashMapWithExpectedSize(multimap.keySet().size()));
114    putAll(multimap);
115  }
116
117  /**
118   * {@inheritDoc}
119   *
120   * <p>Creates an empty {@code HashSet} for a collection of values for one key.
121   *
122   * @return a new {@code HashSet} containing a collection of values for one key
123   */
124  @Override
125  Set<V> createCollection() {
126    return Platform.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
127  }
128
129  /**
130   * @serialData expectedValuesPerKey, number of distinct keys, and then for each distinct key: the
131   *     key, number of values for that key, and the key's values
132   */
133  @GwtIncompatible // java.io.ObjectOutputStream
134  private void writeObject(ObjectOutputStream stream) throws IOException {
135    stream.defaultWriteObject();
136    Serialization.writeMultimap(this, stream);
137  }
138
139  @GwtIncompatible // java.io.ObjectInputStream
140  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
141    stream.defaultReadObject();
142    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
143    int distinctKeys = Serialization.readCount(stream);
144    Map<K, Collection<V>> map = Platform.newHashMapWithExpectedSize(12);
145    setMap(map);
146    Serialization.populateMultimap(this, stream, distinctKeys);
147  }
148
149  @GwtIncompatible // Not needed in emulated source
150  private static final long serialVersionUID = 0;
151}