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.HashMap;
025import org.checkerframework.checker.nullness.qual.Nullable;
026
027/**
028 * Multiset implementation backed by a {@link HashMap}.
029 *
030 * @author Kevin Bourrillion
031 * @author Jared Levy
032 * @since 2.0
033 */
034@GwtCompatible(serializable = true, emulated = true)
035@ElementTypesAreNonnullByDefault
036public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {
037
038  /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
039  public static <E extends @Nullable Object> HashMultiset<E> create() {
040    return new HashMultiset<E>();
041  }
042
043  /**
044   * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
045   * elements.
046   *
047   * @param distinctElements the expected number of distinct elements
048   * @throws IllegalArgumentException if {@code distinctElements} is negative
049   */
050  public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) {
051    return new HashMultiset<E>(distinctElements);
052  }
053
054  /**
055   * Creates a new {@code HashMultiset} containing the specified elements.
056   *
057   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
058   *
059   * @param elements the elements that the multiset should contain
060   */
061  public static <E extends @Nullable Object> HashMultiset<E> create(
062      Iterable<? extends E> elements) {
063    HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
064    Iterables.addAll(multiset, elements);
065    return multiset;
066  }
067
068  private HashMultiset() {
069    super(new HashMap<E, Count>());
070  }
071
072  private HashMultiset(int distinctElements) {
073    super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
074  }
075
076  /**
077   * @serialData the number of distinct elements, the first element, its count, the second element,
078   *     its count, and so on
079   */
080  @GwtIncompatible // java.io.ObjectOutputStream
081  private void writeObject(ObjectOutputStream stream) throws IOException {
082    stream.defaultWriteObject();
083    Serialization.writeMultiset(this, stream);
084  }
085
086  @GwtIncompatible // java.io.ObjectInputStream
087  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
088    stream.defaultReadObject();
089    int distinctElements = Serialization.readCount(stream);
090    setBackingMap(Maps.<E, Count>newHashMap());
091    Serialization.populateMultiset(this, stream, distinctElements);
092  }
093
094  @GwtIncompatible // Not needed in emulated source.
095  private static final long serialVersionUID = 0;
096}