001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.collect.Maps.newLinkedHashMapWithExpectedSize;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.J2ktIncompatible;
024import java.io.IOException;
025import java.io.ObjectInputStream;
026import java.io.ObjectOutputStream;
027import java.util.LinkedHashMap;
028import org.jspecify.annotations.Nullable;
029
030/**
031 * A {@code Multiset} implementation with predictable iteration order. Its iterator orders elements
032 * according to when the first occurrence of the element was added. When the multiset contains
033 * multiple instances of an element, those instances are consecutive in the iteration order. If all
034 * occurrences of an element are removed, after which that element is added to the multiset, the
035 * element will appear at the end of the iteration.
036 *
037 * <p>See the Guava User Guide article on <a href=
038 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multiset">{@code Multiset}</a>.
039 *
040 * @author Kevin Bourrillion
041 * @author Jared Levy
042 * @since 2.0
043 */
044@GwtCompatible
045public final class LinkedHashMultiset<E extends @Nullable Object>
046    extends AbstractMapBasedMultiset<E> {
047
048  /** Creates a new, empty {@code LinkedHashMultiset} using the default initial capacity. */
049  public static <E extends @Nullable Object> LinkedHashMultiset<E> create() {
050    return new LinkedHashMultiset<>();
051  }
052
053  /**
054   * Creates a new, empty {@code LinkedHashMultiset} with the specified expected number of distinct
055   * elements.
056   *
057   * @param distinctElements the expected number of distinct elements
058   * @throws IllegalArgumentException if {@code distinctElements} is negative
059   */
060  public static <E extends @Nullable Object> LinkedHashMultiset<E> create(int distinctElements) {
061    return new LinkedHashMultiset<>(distinctElements);
062  }
063
064  /**
065   * Creates a new {@code LinkedHashMultiset} containing the specified elements.
066   *
067   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
068   *
069   * @param elements the elements that the multiset should contain
070   */
071  public static <E extends @Nullable Object> LinkedHashMultiset<E> create(
072      Iterable<? extends E> elements) {
073    LinkedHashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
074    Iterables.addAll(multiset, elements);
075    return multiset;
076  }
077
078  private LinkedHashMultiset() {
079    super(new LinkedHashMap<E, Count>());
080  }
081
082  private LinkedHashMultiset(int distinctElements) {
083    super(newLinkedHashMapWithExpectedSize(distinctElements));
084  }
085
086  /**
087   * @serialData the number of distinct elements, the first element, its count, the second element,
088   *     its count, and so on
089   */
090  @GwtIncompatible
091  @J2ktIncompatible
092    private void writeObject(ObjectOutputStream stream) throws IOException {
093    stream.defaultWriteObject();
094    Serialization.writeMultiset(this, stream);
095  }
096
097  @GwtIncompatible
098  @J2ktIncompatible
099    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
100    stream.defaultReadObject();
101    int distinctElements = stream.readInt();
102    setBackingMap(new LinkedHashMap<E, Count>());
103    Serialization.populateMultiset(this, stream, distinctElements);
104  }
105
106  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
107}