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 import com.google.common.annotations.GwtIncompatible;
21 import java.io.IOException;
22 import java.io.ObjectInputStream;
23 import java.io.ObjectOutputStream;
24 import java.util.HashMap;
25 import org.checkerframework.checker.nullness.qual.Nullable;
26
27 /**
28 * Multiset implementation backed by a {@link HashMap}.
29 *
30 * @author Kevin Bourrillion
31 * @author Jared Levy
32 * @since 2.0
33 */
34 @GwtCompatible(serializable = true, emulated = true)
35 @ElementTypesAreNonnullByDefault
36 public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {
37
38 /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
39 public static <E extends @Nullable Object> HashMultiset<E> create() {
40 return new HashMultiset<E>();
41 }
42
43 /**
44 * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
45 * elements.
46 *
47 * @param distinctElements the expected number of distinct elements
48 * @throws IllegalArgumentException if {@code distinctElements} is negative
49 */
50 public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) {
51 return new HashMultiset<E>(distinctElements);
52 }
53
54 /**
55 * Creates a new {@code HashMultiset} containing the specified elements.
56 *
57 * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
58 *
59 * @param elements the elements that the multiset should contain
60 */
61 public static <E extends @Nullable Object> HashMultiset<E> create(
62 Iterable<? extends E> elements) {
63 HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
64 Iterables.addAll(multiset, elements);
65 return multiset;
66 }
67
68 private HashMultiset() {
69 super(new HashMap<E, Count>());
70 }
71
72 private HashMultiset(int distinctElements) {
73 super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
74 }
75
76 /**
77 * @serialData the number of distinct elements, the first element, its count, the second element,
78 * its count, and so on
79 */
80 @GwtIncompatible // java.io.ObjectOutputStream
81 private void writeObject(ObjectOutputStream stream) throws IOException {
82 stream.defaultWriteObject();
83 Serialization.writeMultiset(this, stream);
84 }
85
86 @GwtIncompatible // java.io.ObjectInputStream
87 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
88 stream.defaultReadObject();
89 int distinctElements = Serialization.readCount(stream);
90 setBackingMap(Maps.<E, Count>newHashMap());
91 Serialization.populateMultiset(this, stream, distinctElements);
92 }
93
94 @GwtIncompatible // Not needed in emulated source.
95 private static final long serialVersionUID = 0;
96 }