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