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;
021
022import java.io.IOException;
023import java.io.ObjectInputStream;
024import java.io.ObjectOutputStream;
025import java.util.HashMap;
026import java.util.concurrent.atomic.AtomicInteger;
027
028/**
029 * Multiset implementation backed by a {@link HashMap}.
030 *
031 * @author Kevin Bourrillion
032 * @author Jared Levy
033 * @since 2 (imported from Google Collections Library)
034 */
035@GwtCompatible(serializable = true, emulated = true)
036public final class HashMultiset<E> extends AbstractMapBasedMultiset<E> {
037
038  /**
039   * Creates a new, empty {@code HashMultiset} using the default initial
040   * capacity.
041   */
042  public static <E> HashMultiset<E> create() {
043    return new HashMultiset<E>();
044  }
045
046  /**
047   * Creates a new, empty {@code HashMultiset} with the specified expected
048   * number of distinct elements.
049   *
050   * @param distinctElements the expected number of distinct elements
051   * @throws IllegalArgumentException if {@code distinctElements} is negative
052   */
053  public static <E> HashMultiset<E> create(int distinctElements) {
054    return new HashMultiset<E>(distinctElements);
055  }
056
057  /**
058   * Creates a new {@code HashMultiset} containing the specified elements.
059   *
060   * @param elements the elements that the multiset should contain
061   */
062  public static <E> HashMultiset<E> create(Iterable<? extends E> elements) {
063    HashMultiset<E> multiset =
064        create(Multisets.inferDistinctElements(elements));
065    Iterables.addAll(multiset, elements);
066    return multiset;
067  }
068
069  private HashMultiset() {
070    super(new HashMap<E, AtomicInteger>());
071  }
072
073  private HashMultiset(int distinctElements) {
074    super(new HashMap<E, AtomicInteger>(Maps.capacity(distinctElements)));
075  }
076
077  /**
078   * @serialData the number of distinct elements, the first element, its count,
079   *     the second element, its count, and so on
080   */
081  @GwtIncompatible("java.io.ObjectOutputStream")
082  private void writeObject(ObjectOutputStream stream) throws IOException {
083    stream.defaultWriteObject();
084    Serialization.writeMultiset(this, stream);
085  }
086
087  @GwtIncompatible("java.io.ObjectInputStream")
088  private void readObject(ObjectInputStream stream)
089      throws IOException, ClassNotFoundException {
090    stream.defaultReadObject();
091    int distinctElements = Serialization.readCount(stream);
092    setBackingMap(
093        Maps.<E, AtomicInteger>newHashMapWithExpectedSize(distinctElements));
094    Serialization.populateMultiset(this, stream, distinctElements);
095  }
096
097  @GwtIncompatible("Not needed in emulated source.")
098  private static final long serialVersionUID = 0;
099}