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;
021
022import java.io.IOException;
023import java.io.ObjectInputStream;
024import java.io.ObjectOutputStream;
025import java.util.LinkedHashMap;
026
027/**
028 * A {@code Multiset} implementation with predictable iteration order. Its
029 * iterator orders elements according to when the first occurrence of the
030 * element was added. When the multiset contains multiple instances of an
031 * 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
033 * the multiset, the 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">
037 * {@code Multiset}</a>.
038 *
039 * @author Kevin Bourrillion
040 * @author Jared Levy
041 * @since 2.0
042 */
043@GwtCompatible(serializable = true, emulated = true)
044@SuppressWarnings("serial") // we're overriding default serialization
045public final class LinkedHashMultiset<E> extends AbstractMapBasedMultiset<E> {
046
047  /**
048   * Creates a new, empty {@code LinkedHashMultiset} using the default initial
049   * capacity.
050   */
051  public static <E> LinkedHashMultiset<E> create() {
052    return new LinkedHashMultiset<E>();
053  }
054
055  /**
056   * Creates a new, empty {@code LinkedHashMultiset} with the specified expected
057   * number of distinct elements.
058   *
059   * @param distinctElements the expected number of distinct elements
060   * @throws IllegalArgumentException if {@code distinctElements} is negative
061   */
062  public static <E> LinkedHashMultiset<E> create(int distinctElements) {
063    return new LinkedHashMultiset<E>(distinctElements);
064  }
065
066  /**
067   * Creates a new {@code LinkedHashMultiset} containing the specified elements.
068   *
069   * <p>This implementation is highly efficient when {@code elements} is itself
070   * a {@link Multiset}.
071   *
072   * @param elements the elements that the multiset should contain
073   */
074  public static <E> LinkedHashMultiset<E> create(Iterable<? extends E> elements) {
075    LinkedHashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
076    Iterables.addAll(multiset, elements);
077    return multiset;
078  }
079
080  private LinkedHashMultiset() {
081    super(new LinkedHashMap<E, Count>());
082  }
083
084  private LinkedHashMultiset(int distinctElements) {
085    super(Maps.<E, Count>newLinkedHashMapWithExpectedSize(distinctElements));
086  }
087
088  /**
089   * @serialData the number of distinct elements, the first element, its count,
090   *     the second element, its count, and so on
091   */
092  @GwtIncompatible("java.io.ObjectOutputStream")
093  private void writeObject(ObjectOutputStream stream) throws IOException {
094    stream.defaultWriteObject();
095    Serialization.writeMultiset(this, stream);
096  }
097
098  @GwtIncompatible("java.io.ObjectInputStream")
099  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
100    stream.defaultReadObject();
101    int distinctElements = Serialization.readCount(stream);
102    setBackingMap(new LinkedHashMap<E, Count>());
103    Serialization.populateMultiset(this, stream, distinctElements);
104  }
105
106  @GwtIncompatible("not needed in emulated source")
107  private static final long serialVersionUID = 0;
108}