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