Java tutorial
/* * 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.GwtIncompatible; import com.google.common.annotations.VisibleForTesting; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.util.ArrayList; import java.util.Collection; import java.util.HashMap; import java.util.List; import java.util.Map; /** * 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= * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> * {@code Multimap}</a>. * * @author Jared Levy * @since 2.0 */ @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(); } } /** * @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") private void writeObject(ObjectOutputStream stream) throws IOException { stream.defaultWriteObject(); Serialization.writeMultimap(this, stream); } @GwtIncompatible("java.io.ObjectOutputStream") private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException { stream.defaultReadObject(); expectedValuesPerKey = DEFAULT_VALUES_PER_KEY; int distinctKeys = Serialization.readCount(stream); Map<K, Collection<V>> map = Maps.newHashMap(); setMap(map); Serialization.populateMultimap(this, stream, distinctKeys); } @GwtIncompatible("Not needed in emulated source.") private static final long serialVersionUID = 0; }