guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ArrayListMultimap.java

/*
 * 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 static com.google.common.collect.CollectPreconditions.checkNonnegative;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;

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.
 *
 * <p>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.
 *
 * <p>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.
 *
 * <p>Keys and values may be null. All optional multimap methods are supported,
 * and all returned views are modifiable.
 *
 * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link
 * #replaceValues} all implement {@link java.util.RandomAccess}.
 *
 * <p>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}.
 * 
 * <p>See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap">
 * {@code Multimap}</a>.
 *
 * @author Jared Levy
 * @since 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 {@code ArrayListMultimap} with the default initial
   * capacities.
   */
  public static <K, V> ArrayListMultimap<K, V> create() {
    return new ArrayListMultimap<K, V>();
  }

  /**
   * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold
   * the specified numbers of keys and values without resizing.
   *
   * @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 <K, V> ArrayListMultimap<K, V> create(
      int expectedKeys, int expectedValuesPerKey) {
    return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
  }

  /**
   * Constructs an {@code ArrayListMultimap} with the same mappings as the
   * specified multimap.
   *
   * @param 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>>());
    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
  }

  private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
    super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
    checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey");
    this.expectedValuesPerKey = expectedValuesPerKey;
  }

  private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
    this(multimap.keySet().size(),
        (multimap instanceof ArrayListMultimap) ?
            ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey :
            DEFAULT_VALUES_PER_KEY);
    putAll(multimap);
  }

  /**
   * Creates a new, empty {@code ArrayList} to hold the collection of values for
   * an arbitrary key.
   */
  @Override List<V> createCollection() {
    return new ArrayList<V>(expectedValuesPerKey);
  }

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