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