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
17package com.google.common.collect;
18
19import com.google.common.annotations.GwtCompatible;
20
21import 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)
31public 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
76