com.google.common.collect.HashMultimap Maven / Gradle / Ivy
/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.Map;
import java.util.Set;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Implementation of {@link Multimap} using hash tables.
*
* The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an
* existing key-value pair has no effect.
*
*
Keys and values may be null. All optional multimap methods are supported, and all returned
* views are modifiable.
*
*
This class is not threadsafe when any concurrent operations update the multimap. Concurrent
* read operations will work correctly if the last write happens-before any reads. To allow
* concurrent update operations, wrap your multimap with a call to {@link
* Multimaps#synchronizedSetMultimap}.
*
*
Warning: Do not modify either a key or a value of a {@code HashMultimap} in a
* way that affects its {@link Object#equals} behavior. Undefined behavior and bugs will result.
*
* @author Jared Levy
* @since 2.0
*/
@GwtCompatible(serializable = true, emulated = true)
@ElementTypesAreNonnullByDefault
public final class HashMultimap
extends HashMultimapGwtSerializationDependencies {
private static final int DEFAULT_VALUES_PER_KEY = 2;
@VisibleForTesting transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
/**
* Creates a new, empty {@code HashMultimap} with the default initial capacities.
*
* You may also consider the equivalent {@code
* MultimapBuilder.hashKeys().hashSetValues().build()}, which provides more control over the
* underlying data structure.
*/
public static
HashMultimap create() {
return new HashMultimap<>();
}
/**
* Constructs an empty {@code HashMultimap} with enough capacity to hold the specified numbers of
* keys and values without rehashing.
*
* You may also consider the equivalent {@code
* MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build()}, which
* provides more control over the underlying data structure.
*
* @param expectedKeys the expected number of distinct keys
* @param expectedValuesPerKey the expected average number of values per key
* @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
* negative
*/
public static HashMultimap create(
int expectedKeys, int expectedValuesPerKey) {
return new HashMultimap<>(expectedKeys, expectedValuesPerKey);
}
/**
* Constructs a {@code HashMultimap} with the same mappings as the specified multimap. If a
* key-value mapping appears multiple times in the input multimap, it only appears once in the
* constructed multimap.
*
* You may also consider the equivalent {@code
* MultimapBuilder.hashKeys().hashSetValues().build(multimap)}, which provides more control over
* the underlying data structure.
*
* @param multimap the multimap whose contents are copied to this multimap
*/
public static HashMultimap create(
Multimap multimap) {
return new HashMultimap<>(multimap);
}
private HashMultimap() {
this(12, DEFAULT_VALUES_PER_KEY);
}
private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
super(Platform.>newHashMapWithExpectedSize(expectedKeys));
Preconditions.checkArgument(expectedValuesPerKey >= 0);
this.expectedValuesPerKey = expectedValuesPerKey;
}
private HashMultimap(Multimap multimap) {
super(Platform.>newHashMapWithExpectedSize(multimap.keySet().size()));
putAll(multimap);
}
/**
* {@inheritDoc}
*
* Creates an empty {@code HashSet} for a collection of values for one key.
*
* @return a new {@code HashSet} containing a collection of values for one key
*/
@Override
Set createCollection() {
return Platform.newHashSetWithExpectedSize(expectedValuesPerKey);
}
/**
* @serialData expectedValuesPerKey, number of distinct keys, and then for each distinct key: the
* key, number of values for that key, and the key's values
*/
@GwtIncompatible // java.io.ObjectOutputStream
@J2ktIncompatible
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.defaultWriteObject();
Serialization.writeMultimap(this, stream);
}
@GwtIncompatible // java.io.ObjectInputStream
@J2ktIncompatible
private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
stream.defaultReadObject();
expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
int distinctKeys = Serialization.readCount(stream);
Map> map = Platform.newHashMapWithExpectedSize(12);
setMap(map);
Serialization.populateMultimap(this, stream, distinctKeys);
}
@GwtIncompatible // Not needed in emulated source
@J2ktIncompatible
private static final long serialVersionUID = 0;
}