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.HashMap;
026import org.jspecify.annotations.Nullable;
027
028/**
029 * Multiset implementation backed by a {@link HashMap}.
030 *
031 * @author Kevin Bourrillion
032 * @author Jared Levy
033 * @since 2.0
034 */
035@GwtCompatible(serializable = true, emulated = true)
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<>();
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<>(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  @J2ktIncompatible
082  private void writeObject(ObjectOutputStream stream) throws IOException {
083    stream.defaultWriteObject();
084    Serialization.writeMultiset(this, stream);
085  }
086
087  @GwtIncompatible // java.io.ObjectInputStream
088  @J2ktIncompatible
089  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
090    stream.defaultReadObject();
091    int distinctElements = Serialization.readCount(stream);
092    setBackingMap(Maps.<E, Count>newHashMap());
093    Serialization.populateMultiset(this, stream, distinctElements);
094  }
095
096  @GwtIncompatible // Not needed in emulated source.
097  @J2ktIncompatible
098  private static final long serialVersionUID = 0;
099}