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   * 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
  * 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.
 import static;
 import java.util.List;
 import java.util.Map;

Implementation of Multimap that uses an ArrayList to store the values for a given key. A java.util.HashMap associates each key with an java.util.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 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.

The lists returned by AbstractListMultimap.get(java.lang.Object), AbstractListMultimap.removeAll(java.lang.Object), and AbstractListMultimap.replaceValues(java.lang.Object,java.lang.Iterable) all implement java.util.RandomAccess.

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 Multimaps.synchronizedListMultimap(

See the Guava User Guide article on Multimap.

Jared Levy
2.0 (imported from Google Collections Library)
 @GwtCompatible(serializable = true, emulated = true)
 public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
   // Default from ArrayList
   private static final int DEFAULT_VALUES_PER_KEY = 3;
   @VisibleForTesting transient int expectedValuesPerKey;

Creates a new, empty ArrayListMultimap with the default initial capacities.
   public static <K, V> ArrayListMultimap<K, V> create() {
     return new ArrayListMultimap<K, V>();

Constructs an empty ArrayListMultimap with enough capacity to hold the specified numbers of keys and values without resizing.

expectedKeys the expected number of distinct keys
expectedValuesPerKey the expected average number of values per key
java.lang.IllegalArgumentException if expectedKeys or expectedValuesPerKey is negative
   public static <K, V> ArrayListMultimap<K, V> create(
       int expectedKeysint expectedValuesPerKey) {
     return new ArrayListMultimap<K, V>(expectedKeysexpectedValuesPerKey);

Constructs an ArrayListMultimap with the same mappings as the specified multimap.

multimap the multimap whose contents are copied to this multimap
  public static <K, V> ArrayListMultimap<K, V> create(
      Multimap<? extends K, ? extends V> multimap) {
    return new ArrayListMultimap<K, V>(multimap);
  private ArrayListMultimap() {
    super(new HashMap<K, Collection<V>>());
  private ArrayListMultimap(int expectedKeysint expectedValuesPerKey) {
    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
    checkArgument(expectedValuesPerKey >= 0);
    this. = expectedValuesPerKey;
  private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
        (multimap instanceof ArrayListMultimap) ?
            ((ArrayListMultimap<?, ?>) multimap). :

Creates a new, empty ArrayList to hold the collection of values for an arbitrary key.
    return new ArrayList<V>();

Reduces the memory used by this ArrayListMultimap, if feasible.
  public void trimToSize() {
    for (Collection<V> collection : backingMap().values()) {
      ArrayList<V> arrayList = (ArrayList<V>) collection;


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 streamthrows IOException {
  private void readObject(ObjectInputStream stream)
      throws IOExceptionClassNotFoundException {
     = stream.readInt();
    int distinctKeys = Serialization.readCount(stream);
    Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
  @GwtIncompatible("Not needed in emulated source.")
  private static final long serialVersionUID = 0;
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