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.checkerframework.checker.nullness.qual.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)
036@ElementTypesAreNonnullByDefault
037public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {
038
039  /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
040  public static <E extends @Nullable Object> HashMultiset<E> create() {
041    return new HashMultiset<>();
042  }
043
044  /**
045   * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
046   * elements.
047   *
048   * @param distinctElements the expected number of distinct elements
049   * @throws IllegalArgumentException if {@code distinctElements} is negative
050   */
051  public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) {
052    return new HashMultiset<>(distinctElements);
053  }
054
055  /**
056   * Creates a new {@code HashMultiset} containing the specified elements.
057   *
058   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
059   *
060   * @param elements the elements that the multiset should contain
061   */
062  public static <E extends @Nullable Object> HashMultiset<E> create(
063      Iterable<? extends E> elements) {
064    HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
065    Iterables.addAll(multiset, elements);
066    return multiset;
067  }
068
069  private HashMultiset() {
070    super(new HashMap<E, Count>());
071  }
072
073  private HashMultiset(int distinctElements) {
074    super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements));
075  }
076
077  /**
078   * @serialData the number of distinct elements, the first element, its count, the second element,
079   *     its count, and so on
080   */
081  @GwtIncompatible // java.io.ObjectOutputStream
082  @J2ktIncompatible
083  private void writeObject(ObjectOutputStream stream) throws IOException {
084    stream.defaultWriteObject();
085    Serialization.writeMultiset(this, stream);
086  }
087
088  @GwtIncompatible // java.io.ObjectInputStream
089  @J2ktIncompatible
090  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
091    stream.defaultReadObject();
092    int distinctElements = Serialization.readCount(stream);
093    setBackingMap(Maps.<E, Count>newHashMap());
094    Serialization.populateMultiset(this, stream, distinctElements);
095  }
096
097  @GwtIncompatible // Not needed in emulated source.
098  @J2ktIncompatible
099  private static final long serialVersionUID = 0;
100}