    001    /*
    002     * Copyright (C) 2007 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.collect;
    018
    019    import static com.google.common.base.Preconditions.checkArgument;
    020
    021    import com.google.common.annotations.GwtCompatible;
    022    import com.google.common.annotations.GwtIncompatible;
    023    import com.google.common.annotations.VisibleForTesting;
    024
    025    import java.io.IOException;
    026    import java.io.ObjectInputStream;
    027    import java.io.ObjectOutputStream;
    028    import java.util.ArrayList;
    029    import java.util.Collection;
    030    import java.util.HashMap;
    031    import java.util.List;
    032    import java.util.Map;
    033
    034    /**
    035     * Implementation of {@code Multimap} that uses an {@code ArrayList} to store
    036     * the values for a given key. A {@link HashMap} associates each key with an
    037     * {@link ArrayList} of values.
    038     *
    039     * <p>When iterating through the collections supplied by this class, the
    040     * ordering of values for a given key agrees with the order in which the values
    041     * were added.
    042     *
    043     * <p>This multimap allows duplicate key-value pairs. After adding a new
    044     * key-value pair equal to an existing key-value pair, the {@code
    045     * ArrayListMultimap} will contain entries for both the new value and the old
    046     * value.
    047     *
    048     * <p>Keys and values may be null. All optional multimap methods are supported,
    049     * and all returned views are modifiable.
    050     *
    051     * <p>The lists returned by {@link #get}, {@link #removeAll}, and {@link
    052     * #replaceValues} all implement {@link java.util.RandomAccess}.
    053     *
    054     * <p>This class is not threadsafe when any concurrent operations update the
    055     * multimap. Concurrent read operations will work correctly. To allow concurrent
    056     * update operations, wrap your multimap with a call to {@link
    057     * Multimaps#synchronizedListMultimap}.
    058     *
    059     * @author Jared Levy
    060     * @since 2.0 (imported from Google Collections Library)
    061     */
    062    @GwtCompatible(serializable = true, emulated = true)
    063    public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
    064      // Default from ArrayList
    065      private static final int DEFAULT_VALUES_PER_KEY = 10;
    066
    067      @VisibleForTesting transient int expectedValuesPerKey;
    068
    069      /**
    070       * Creates a new, empty {@code ArrayListMultimap} with the default initial
    071       * capacities.
    072       */
    073      public static <K, V> ArrayListMultimap<K, V> create() {
    074        return new ArrayListMultimap<K, V>();
    075      }
    076
    077      /**
    078       * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold
    079       * the specified numbers of keys and values without resizing.
    080       *
    081       * @param expectedKeys the expected number of distinct keys
    082       * @param expectedValuesPerKey the expected average number of values per key
    083       * @throws IllegalArgumentException if {@code expectedKeys} or {@code
    084       *      expectedValuesPerKey} is negative
    085       */
    086      public static <K, V> ArrayListMultimap<K, V> create(
    087          int expectedKeys, int expectedValuesPerKey) {
    088        return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
    089      }
    090
    091      /**
    092       * Constructs an {@code ArrayListMultimap} with the same mappings as the
    093       * specified multimap.
    094       *
    095       * @param multimap the multimap whose contents are copied to this multimap
    096       */
    097      public static <K, V> ArrayListMultimap<K, V> create(
    098          Multimap<? extends K, ? extends V> multimap) {
    099        return new ArrayListMultimap<K, V>(multimap);
    100      }
    101
    102      private ArrayListMultimap() {
    103        super(new HashMap<K, Collection<V>>());
    104        expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    105      }
    106
    107      private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
    108        super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
    109        checkArgument(expectedValuesPerKey >= 0);
    110        this.expectedValuesPerKey = expectedValuesPerKey;
    111      }
    112
    113      private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
    114        this(multimap.keySet().size(),
    115            (multimap instanceof ArrayListMultimap) ?
    116                ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey :
    117                DEFAULT_VALUES_PER_KEY);
    118        putAll(multimap);
    119      }
    120
    121      /**
    122       * Creates a new, empty {@code ArrayList} to hold the collection of values for
    123       * an arbitrary key.
    124       */
    125      @Override List<V> createCollection() {
    126        return new ArrayList<V>(expectedValuesPerKey);
    127      }
    128
    129      /**
    130       * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
    131       */
    132      public void trimToSize() {
    133        for (Collection<V> collection : backingMap().values()) {
    134          ArrayList<V> arrayList = (ArrayList<V>) collection;
    135          arrayList.trimToSize();
    136        }
    137      }
    138
    139      /**
    140       * @serialData expectedValuesPerKey, number of distinct keys, and then for
    141       *     each distinct key: the key, number of values for that key, and the
    142       *     key's values
    143       */
    144      @GwtIncompatible("java.io.ObjectOutputStream")
    145      private void writeObject(ObjectOutputStream stream) throws IOException {
    146        stream.defaultWriteObject();
    147        stream.writeInt(expectedValuesPerKey);
    148        Serialization.writeMultimap(this, stream);
    149      }
    150
    151      @GwtIncompatible("java.io.ObjectOutputStream")
    152      private void readObject(ObjectInputStream stream)
    153          throws IOException, ClassNotFoundException {
    154        stream.defaultReadObject();
    155        expectedValuesPerKey = stream.readInt();
    156        int distinctKeys = Serialization.readCount(stream);
    157        Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
    158        setMap(map);
    159        Serialization.populateMultimap(this, stream, distinctKeys);
    160      }
    161
    162      @GwtIncompatible("Not needed in emulated source.")
    163      private static final long serialVersionUID = 0;
    164    }