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 org.checkerframework.checker.nullness.qual.Nullable;
023
024/**
025 * Multiset implementation that uses hashing for key and entry access.
026 *
027 * @author Kevin Bourrillion
028 * @author Jared Levy
029 * @since 2.0
030 */
031@GwtCompatible(serializable = true, emulated = true)
032@ElementTypesAreNonnullByDefault
033public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {
034
035  /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
036  public static <E extends @Nullable Object> HashMultiset<E> create() {
037    return create(ObjectCountHashMap.DEFAULT_SIZE);
038  }
039
040  /**
041   * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
042   * elements.
043   *
044   * @param distinctElements the expected number of distinct elements
045   * @throws IllegalArgumentException if {@code distinctElements} is negative
046   */
047  public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) {
048    return new HashMultiset<E>(distinctElements);
049  }
050
051  /**
052   * Creates a new {@code HashMultiset} containing the specified elements.
053   *
054   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
055   *
056   * @param elements the elements that the multiset should contain
057   */
058  public static <E extends @Nullable Object> HashMultiset<E> create(
059      Iterable<? extends E> elements) {
060    HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
061    Iterables.addAll(multiset, elements);
062    return multiset;
063  }
064
065  HashMultiset(int distinctElements) {
066    super(distinctElements);
067  }
068
069  @Override
070  ObjectCountHashMap<E> newBackingMap(int distinctElements) {
071    return new ObjectCountHashMap<>(distinctElements);
072  }
073
074  @GwtIncompatible // Not needed in emulated source.
075  @J2ktIncompatible
076  private static final long serialVersionUID = 0;
077}