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 com.google.common.annotations.GwtCompatible;
020import com.google.common.annotations.GwtIncompatible;
021import com.google.common.annotations.J2ktIncompatible;
022import java.io.IOException;
023import java.io.ObjectInputStream;
024import java.io.ObjectOutputStream;
025import java.util.LinkedHashMap;
026import org.jspecify.annotations.Nullable;
027
028/**
029 * A {@code Multiset} implementation with predictable iteration order. Its iterator orders elements
030 * according to when the first occurrence of the element was added. When the multiset contains
031 * multiple instances of an element, those instances are consecutive in the iteration order. If all
032 * occurrences of an element are removed, after which that element is added to the multiset, the
033 * element will appear at the end of the iteration.
034 *
035 * <p>See the Guava User Guide article on <a href=
036 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multiset">{@code Multiset}</a>.
037 *
038 * @author Kevin Bourrillion
039 * @author Jared Levy
040 * @since 2.0
041 */
042@GwtCompatible(serializable = true, emulated = true)
043public final class LinkedHashMultiset<E extends @Nullable Object>
044    extends AbstractMapBasedMultiset<E> {
045
046  /** Creates a new, empty {@code LinkedHashMultiset} using the default initial capacity. */
047  public static <E extends @Nullable Object> LinkedHashMultiset<E> create() {
048    return new LinkedHashMultiset<>();
049  }
050
051  /**
052   * Creates a new, empty {@code LinkedHashMultiset} with the specified expected number of distinct
053   * elements.
054   *
055   * @param distinctElements the expected number of distinct elements
056   * @throws IllegalArgumentException if {@code distinctElements} is negative
057   */
058  public static <E extends @Nullable Object> LinkedHashMultiset<E> create(int distinctElements) {
059    return new LinkedHashMultiset<>(distinctElements);
060  }
061
062  /**
063   * Creates a new {@code LinkedHashMultiset} containing the specified elements.
064   *
065   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
066   *
067   * @param elements the elements that the multiset should contain
068   */
069  public static <E extends @Nullable Object> LinkedHashMultiset<E> create(
070      Iterable<? extends E> elements) {
071    LinkedHashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
072    Iterables.addAll(multiset, elements);
073    return multiset;
074  }
075
076  private LinkedHashMultiset() {
077    super(new LinkedHashMap<E, Count>());
078  }
079
080  private LinkedHashMultiset(int distinctElements) {
081    super(Maps.<E, Count>newLinkedHashMapWithExpectedSize(distinctElements));
082  }
083
084  /**
085   * @serialData the number of distinct elements, the first element, its count, the second element,
086   *     its count, and so on
087   */
088  @GwtIncompatible // java.io.ObjectOutputStream
089  @J2ktIncompatible
090  private void writeObject(ObjectOutputStream stream) throws IOException {
091    stream.defaultWriteObject();
092    Serialization.writeMultiset(this, stream);
093  }
094
095  @GwtIncompatible // java.io.ObjectInputStream
096  @J2ktIncompatible
097  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
098    stream.defaultReadObject();
099    int distinctElements = Serialization.readCount(stream);
100    setBackingMap(new LinkedHashMap<E, Count>());
101    Serialization.populateMultiset(this, stream, distinctElements);
102  }
103
104  @GwtIncompatible // not needed in emulated source
105  @J2ktIncompatible
106  private static final long serialVersionUID = 0;
107}