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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 
     21 import java.io.IOException;
     22 import java.io.ObjectInputStream;
     23 import java.io.ObjectOutputStream;
     24 import java.util.HashMap;
     25 import java.util.concurrent.atomic.AtomicInteger;
     26 
     27 /**
     28  * Multiset implementation backed by a {@link HashMap}.
     29  *
     30  * @author Kevin Bourrillion
     31  * @author Jared Levy
     32  * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
     33  */
     34 @GwtCompatible(serializable = true)
     35 public final class HashMultiset<E> extends AbstractMapBasedMultiset<E> {
     36 
     37   /**
     38    * Creates a new, empty {@code HashMultiset} using the default initial
     39    * capacity.
     40    */
     41   public static <E> HashMultiset<E> create() {
     42     return new HashMultiset<E>();
     43   }
     44 
     45   /**
     46    * Creates a new, empty {@code HashMultiset} with the specified expected
     47    * number of distinct elements.
     48    *
     49    * @param distinctElements the expected number of distinct elements
     50    * @throws IllegalArgumentException if {@code distinctElements} is negative
     51    */
     52   public static <E> HashMultiset<E> create(int distinctElements) {
     53     return new HashMultiset<E>(distinctElements);
     54   }
     55 
     56   /**
     57    * Creates a new {@code HashMultiset} containing the specified elements.
     58    *
     59    * @param elements the elements that the multiset should contain
     60    */
     61   public static <E> HashMultiset<E> create(Iterable<? extends E> elements) {
     62     HashMultiset<E> multiset =
     63         create(Multisets.inferDistinctElements(elements));
     64     Iterables.addAll(multiset, elements);
     65     return multiset;
     66   }
     67 
     68   private HashMultiset() {
     69     super(new HashMap<E, AtomicInteger>());
     70   }
     71 
     72   private HashMultiset(int distinctElements) {
     73     super(new HashMap<E, AtomicInteger>(Maps.capacity(distinctElements)));
     74   }
     75 
     76   /**
     77    * @serialData the number of distinct elements, the first element, its count,
     78    *     the second element, its count, and so on
     79    */
     80   private void writeObject(ObjectOutputStream stream) throws IOException {
     81     stream.defaultWriteObject();
     82     Serialization.writeMultiset(this, stream);
     83   }
     84 
     85   private void readObject(ObjectInputStream stream)
     86       throws IOException, ClassNotFoundException {
     87     stream.defaultReadObject();
     88     int distinctElements = Serialization.readCount(stream);
     89     setBackingMap(
     90         Maps.<E, AtomicInteger>newHashMapWithExpectedSize(distinctElements));
     91     Serialization.populateMultiset(this, stream, distinctElements);
     92   }
     93 
     94   private static final long serialVersionUID = 0;
     95 }
     96