    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     * <p>See the Guava User Guide article on <a href=
    060     * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap">
    061     * {@code Multimap}</a>.
    062     *
    063     * @author Jared Levy
    064     * @since 2.0 (imported from Google Collections Library)
    065     */
    066    @GwtCompatible(serializable = true, emulated = true)
    067    public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
    068      // Default from ArrayList
    069      private static final int DEFAULT_VALUES_PER_KEY = 3;
    070
    071      @VisibleForTesting transient int expectedValuesPerKey;
    072
    073      /**
    074       * Creates a new, empty {@code ArrayListMultimap} with the default initial
    075       * capacities.
    076       */
    077      public static <K, V> ArrayListMultimap<K, V> create() {
    078        return new ArrayListMultimap<K, V>();
    079      }
    080
    081      /**
    082       * Constructs an empty {@code ArrayListMultimap} with enough capacity to hold
    083       * the specified numbers of keys and values without resizing.
    084       *
    085       * @param expectedKeys the expected number of distinct keys
    086       * @param expectedValuesPerKey the expected average number of values per key
    087       * @throws IllegalArgumentException if {@code expectedKeys} or {@code
    088       *      expectedValuesPerKey} is negative
    089       */
    090      public static <K, V> ArrayListMultimap<K, V> create(
    091          int expectedKeys, int expectedValuesPerKey) {
    092        return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
    093      }
    094
    095      /**
    096       * Constructs an {@code ArrayListMultimap} with the same mappings as the
    097       * specified multimap.
    098       *
    099       * @param multimap the multimap whose contents are copied to this multimap
    100       */
    101      public static <K, V> ArrayListMultimap<K, V> create(
    102          Multimap<? extends K, ? extends V> multimap) {
    103        return new ArrayListMultimap<K, V>(multimap);
    104      }
    105
    106      private ArrayListMultimap() {
    107        super(new HashMap<K, Collection<V>>());
    108        expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    109      }
    110
    111      private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
    112        super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
    113        checkArgument(expectedValuesPerKey >= 0);
    114        this.expectedValuesPerKey = expectedValuesPerKey;
    115      }
    116
    117      private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
    118        this(multimap.keySet().size(),
    119            (multimap instanceof ArrayListMultimap) ?
    120                ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey :
    121                DEFAULT_VALUES_PER_KEY);
    122        putAll(multimap);
    123      }
    124
    125      /**
    126       * Creates a new, empty {@code ArrayList} to hold the collection of values for
    127       * an arbitrary key.
    128       */
    129      @Override List<V> createCollection() {
    130        return new ArrayList<V>(expectedValuesPerKey);
    131      }
    132
    133      /**
    134       * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
    135       */
    136      public void trimToSize() {
    137        for (Collection<V> collection : backingMap().values()) {
    138          ArrayList<V> arrayList = (ArrayList<V>) collection;
    139          arrayList.trimToSize();
    140        }
    141      }
    142
    143      /**
    144       * @serialData expectedValuesPerKey, number of distinct keys, and then for
    145       *     each distinct key: the key, number of values for that key, and the
    146       *     key's values
    147       */
    148      @GwtIncompatible("java.io.ObjectOutputStream")
    149      private void writeObject(ObjectOutputStream stream) throws IOException {
    150        stream.defaultWriteObject();
    151        stream.writeInt(expectedValuesPerKey);
    152        Serialization.writeMultimap(this, stream);
    153      }
    154
    155      @GwtIncompatible("java.io.ObjectOutputStream")
    156      private void readObject(ObjectInputStream stream)
    157          throws IOException, ClassNotFoundException {
    158        stream.defaultReadObject();
    159        expectedValuesPerKey = stream.readInt();
    160        int distinctKeys = Serialization.readCount(stream);
    161        Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
    162        setMap(map);
    163        Serialization.populateMultimap(this, stream, distinctKeys);
    164      }
    165
    166      @GwtIncompatible("Not needed in emulated source.")
    167      private static final long serialVersionUID = 0;
    168    }