com.google.common.collect.HashMultimap Maven / Gradle / Ivy
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/*
* Copyright (C) 2007 Google Inc.
*
* 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.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.HashMap;
import java.util.Map;
import java.util.Set;
/**
* 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. To allow concurrent
* update operations, wrap your multimap with a call to {@link
* Multimaps#synchronizedSetMultimap}.
*
* @author Jared Levy
*/
@GwtCompatible
public final class HashMultimap extends StandardSetMultimap {
private static final int DEFAULT_VALUES_PER_KEY = 8;
@VisibleForTesting
transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
/**
* Creates a new empty {@code HashMultimap} with the default initial
* capacities.
*/
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.
*
* @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.
*
* @param multimap the multimap whose contents are copied to this multimap
*/
public static HashMultimap create(
Multimap multimap) {
return new HashMultimap(multimap);
}
/** Constructs an empty {@code HashMultimap}. */
private HashMultimap() {
super(new HashMap>());
}
/**
* Constructs an empty {@code HashMultimap} with enough capacity to hold the
* specified numbers of keys and values without rehashing.
*/
private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
super(Maps.>newHashMapWithExpectedSize(expectedKeys));
Preconditions.checkArgument(expectedValuesPerKey >= 0);
this.expectedValuesPerKey = 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.
*
* @param multimap the multimap whose contents are copied to this multimap.
*/
private HashMultimap(Multimap multimap) {
super(Maps.>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 Sets.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
*/
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.defaultWriteObject();
stream.writeInt(expectedValuesPerKey);
Serialization.writeMultimap(this, stream);
}
private void readObject(ObjectInputStream stream)
throws IOException, ClassNotFoundException {
stream.defaultReadObject();
expectedValuesPerKey = stream.readInt();
int distinctKeys = Serialization.readCount(stream);
Map> map = Maps.newHashMapWithExpectedSize(distinctKeys);
setMap(map);
Serialization.populateMultimap(this, stream, distinctKeys);
}
private static final long serialVersionUID = 0;
}