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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 static com.google.common.base.Preconditions.checkArgument;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
/**
* Implementation of {@code Multimap} that uses an {@code ArrayList} to store
* the values for a given key. A {@link HashMap} associates each key with an
* {@link ArrayList} of values.
*
* When iterating through the collections supplied by this class, the
* ordering of values for a given key agrees with the order in which the values
* were added.
*
*
This multimap allows duplicate key-value pairs. After adding a new
* key-value pair equal to an existing key-value pair, the {@code
* ArrayListMultimap} will contain entries for both the new value and the old
* value.
*
*
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#synchronizedListMultimap}.
*
* @author Jared Levy
*/
public final class ArrayListMultimap extends StandardListMultimap {
// Default from ArrayList
/*@VisibleForTesting*/ static final int DEFAULT_CAPACITY = 10;
/*@VisibleForTesting*/ final int initialListCapacity;
/** Constructs an empty {@code ArrayListMultimap}. */
public ArrayListMultimap() {
super(new HashMap>());
initialListCapacity = DEFAULT_CAPACITY;
}
/**
* Constructs an empty {@code ArrayListMultimap} with the expected number of
* distinct keys and the expected number of values per distinct key.
*
* @param distinctKeys the expected number of distinct keys
* @param valuesPerKey the expected number of values per distinct key
* @throws IllegalArgumentException if either argument is negative
*/
public ArrayListMultimap(int distinctKeys, int valuesPerKey) {
super(new HashMap>(Maps.capacity(distinctKeys)));
checkArgument(valuesPerKey >= 0);
initialListCapacity = valuesPerKey;
}
/**
* Constructs an {@code ArrayListMultimap} with the same mappings as the
* specified {@code Multimap}.
*/
public ArrayListMultimap(Multimap multimap) {
this(multimap.keySet().size(),
(multimap instanceof ArrayListMultimap) ?
((ArrayListMultimap) multimap).initialListCapacity :
DEFAULT_CAPACITY);
putAll(multimap);
}
/**
* Creates a new empty {@code ArrayList} to hold the collection of values for
* an arbitrary key.
*/
@Override List createCollection() {
return new ArrayList(initialListCapacity);
}
/**
* Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
*/
public void trimToSize() {
for (Collection collection : backingMap().values()) {
ArrayList arrayList = (ArrayList) collection;
arrayList.trimToSize();
}
}
private static final long serialVersionUID = -3840170139986607881L;
}