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      1 /*
      2  * Copyright (C) 2007 Google Inc.
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  * http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.google.common.collect;
     18 
     19 import com.google.common.annotations.GwtCompatible;
     20 import com.google.common.annotations.VisibleForTesting;
     21 import com.google.common.base.Preconditions;
     22 
     23 import java.io.IOException;
     24 import java.io.ObjectInputStream;
     25 import java.io.ObjectOutputStream;
     26 import java.util.Collection;
     27 import java.util.HashMap;
     28 import java.util.Map;
     29 import java.util.Set;
     30 
     31 /**
     32  * Implementation of {@link Multimap} using hash tables.
     33  *
     34  * <p>The multimap does not store duplicate key-value pairs. Adding a new
     35  * key-value pair equal to an existing key-value pair has no effect.
     36  *
     37  * <p>Keys and values may be null. All optional multimap methods are supported,
     38  * and all returned views are modifiable.
     39  *
     40  * <p>This class is not threadsafe when any concurrent operations update the
     41  * multimap. Concurrent read operations will work correctly. To allow concurrent
     42  * update operations, wrap your multimap with a call to {@link
     43  * Multimaps#synchronizedSetMultimap}.
     44  *
     45  * @author Jared Levy
     46  * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
     47  */
     48 @GwtCompatible(serializable = true)
     49 public final class HashMultimap<K, V> extends AbstractSetMultimap<K, V> {
     50   private static final int DEFAULT_VALUES_PER_KEY = 8;
     51 
     52   @VisibleForTesting
     53   transient int expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
     54 
     55   /**
     56    * Creates a new, empty {@code HashMultimap} with the default initial
     57    * capacities.
     58    */
     59   public static <K, V> HashMultimap<K, V> create() {
     60     return new HashMultimap<K, V>();
     61   }
     62 
     63   /**
     64    * Constructs an empty {@code HashMultimap} with enough capacity to hold the
     65    * specified numbers of keys and values without rehashing.
     66    *
     67    * @param expectedKeys the expected number of distinct keys
     68    * @param expectedValuesPerKey the expected average number of values per key
     69    * @throws IllegalArgumentException if {@code expectedKeys} or {@code
     70    *      expectedValuesPerKey} is negative
     71    */
     72   public static <K, V> HashMultimap<K, V> create(
     73       int expectedKeys, int expectedValuesPerKey) {
     74     return new HashMultimap<K, V>(expectedKeys, expectedValuesPerKey);
     75   }
     76 
     77   /**
     78    * Constructs a {@code HashMultimap} with the same mappings as the specified
     79    * multimap. If a key-value mapping appears multiple times in the input
     80    * multimap, it only appears once in the constructed multimap.
     81    *
     82    * @param multimap the multimap whose contents are copied to this multimap
     83    */
     84   public static <K, V> HashMultimap<K, V> create(
     85       Multimap<? extends K, ? extends V> multimap) {
     86     return new HashMultimap<K, V>(multimap);
     87   }
     88 
     89   private HashMultimap() {
     90     super(new HashMap<K, Collection<V>>());
     91   }
     92 
     93   private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
     94     super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(expectedKeys));
     95     Preconditions.checkArgument(expectedValuesPerKey >= 0);
     96     this.expectedValuesPerKey = expectedValuesPerKey;
     97   }
     98 
     99   private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
    100     super(Maps.<K, Collection<V>>newHashMapWithExpectedSize(
    101         multimap.keySet().size()));
    102     putAll(multimap);
    103   }
    104 
    105   /**
    106    * {@inheritDoc}
    107    *
    108    * <p>Creates an empty {@code HashSet} for a collection of values for one key.
    109    *
    110    * @return a new {@code HashSet} containing a collection of values for one key
    111    */
    112   @Override Set<V> createCollection() {
    113     return Sets.<V>newHashSetWithExpectedSize(expectedValuesPerKey);
    114   }
    115 
    116   /**
    117    * @serialData expectedValuesPerKey, number of distinct keys, and then for
    118    *     each distinct key: the key, number of values for that key, and the
    119    *     key's values
    120    */
    121   private void writeObject(ObjectOutputStream stream) throws IOException {
    122     stream.defaultWriteObject();
    123     stream.writeInt(expectedValuesPerKey);
    124     Serialization.writeMultimap(this, stream);
    125   }
    126 
    127   private void readObject(ObjectInputStream stream)
    128       throws IOException, ClassNotFoundException {
    129     stream.defaultReadObject();
    130     expectedValuesPerKey = stream.readInt();
    131     int distinctKeys = Serialization.readCount(stream);
    132     Map<K, Collection<V>> map = Maps.newHashMapWithExpectedSize(distinctKeys);
    133     setMap(map);
    134     Serialization.populateMultimap(this, stream, distinctKeys);
    135   }
    136 
    137   private static final long serialVersionUID = 0;
    138 }
    139