1   /*
2    * Copyright (C) 2007 The Guava Authors
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.util.HashMap;
22  
23  /**
24   * Multiset implementation backed by a {@link HashMap}.
25   *
26   * @author Kevin Bourrillion
27   * @author Jared Levy
28   * @since 2.0 (imported from Google Collections Library)
29   */
30  @GwtCompatible(serializable = true, emulated = true)
31  public final class HashMultiset<E> extends AbstractMapBasedMultiset<E> {
32  
33    /**
34     * Creates a new, empty {@code HashMultiset} using the default initial
35     * capacity.
36     */
37    public static <E> HashMultiset<E> create() {
38      return new HashMultiset<E>();
39    }
40  
41    /**
42     * Creates a new, empty {@code HashMultiset} with the specified expected
43     * number of distinct elements.
44     *
45     * @param distinctElements the expected number of distinct elements
46     * @throws IllegalArgumentException if {@code distinctElements} is negative
47     */
48    public static <E> HashMultiset<E> create(int distinctElements) {
49      return new HashMultiset<E>(distinctElements);
50    }
51  
52    /**
53     * Creates a new {@code HashMultiset} containing the specified elements.
54     * 
55     * <p>This implementation is highly efficient when {@code elements} is itself
56     * a {@link Multiset}.
57     * 
58     * @param elements the elements that the multiset should contain
59     */
60    public static <E> HashMultiset<E> create(Iterable<? extends E> elements) {
61      HashMultiset<E> multiset =
62          create(Multisets.inferDistinctElements(elements));
63      Iterables.addAll(multiset, elements);
64      return multiset;
65    }
66  
67    private HashMultiset() {
68      super(new HashMap<E, Count>());
69    }
70  
71    private HashMultiset(int distinctElements) {
72      super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
73    }
74  }
75