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.LinkedHashMap;
25 import org.checkerframework.checker.nullness.qual.Nullable;
26
27 /**
28 * A {@code Multiset} implementation with predictable iteration order. Its iterator orders elements
29 * according to when the first occurrence of the element was added. When the multiset contains
30 * multiple instances of an element, those instances are consecutive in the iteration order. If all
31 * occurrences of an element are removed, after which that element is added to the multiset, the
32 * element will appear at the end of the iteration.
33 *
34 * <p>See the Guava User Guide article on <a href=
35 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multiset"> {@code
36 * Multiset}</a>.
37 *
38 * @author Kevin Bourrillion
39 * @author Jared Levy
40 * @since 2.0
41 */
42 @GwtCompatible(serializable = true, emulated = true)
43 @ElementTypesAreNonnullByDefault
44 public final class LinkedHashMultiset<E extends @Nullable Object>
45 extends AbstractMapBasedMultiset<E> {
46
47 /** Creates a new, empty {@code LinkedHashMultiset} using the default initial capacity. */
48 public static <E extends @Nullable Object> LinkedHashMultiset<E> create() {
49 return new LinkedHashMultiset<E>();
50 }
51
52 /**
53 * Creates a new, empty {@code LinkedHashMultiset} with the specified expected number of distinct
54 * elements.
55 *
56 * @param distinctElements the expected number of distinct elements
57 * @throws IllegalArgumentException if {@code distinctElements} is negative
58 */
59 public static <E extends @Nullable Object> LinkedHashMultiset<E> create(int distinctElements) {
60 return new LinkedHashMultiset<E>(distinctElements);
61 }
62
63 /**
64 * Creates a new {@code LinkedHashMultiset} containing the specified elements.
65 *
66 * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
67 *
68 * @param elements the elements that the multiset should contain
69 */
70 public static <E extends @Nullable Object> LinkedHashMultiset<E> create(
71 Iterable<? extends E> elements) {
72 LinkedHashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
73 Iterables.addAll(multiset, elements);
74 return multiset;
75 }
76
77 private LinkedHashMultiset() {
78 super(new LinkedHashMap<E, Count>());
79 }
80
81 private LinkedHashMultiset(int distinctElements) {
82 super(Maps.<E, Count>newLinkedHashMapWithExpectedSize(distinctElements));
83 }
84
85 /**
86 * @serialData the number of distinct elements, the first element, its count, the second element,
87 * its count, and so on
88 */
89 @GwtIncompatible // java.io.ObjectOutputStream
90 private void writeObject(ObjectOutputStream stream) throws IOException {
91 stream.defaultWriteObject();
92 Serialization.writeMultiset(this, stream);
93 }
94
95 @GwtIncompatible // java.io.ObjectInputStream
96 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
97 stream.defaultReadObject();
98 int distinctElements = Serialization.readCount(stream);
99 setBackingMap(new LinkedHashMap<E, Count>());
100 Serialization.populateMultiset(this, stream, distinctElements);
101 }
102
103 @GwtIncompatible // not needed in emulated source
104 private static final long serialVersionUID = 0;
105 }