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)
032public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {
033
034  /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
035  public static <E extends @Nullable Object> HashMultiset<E> create() {
036    return create(ObjectCountHashMap.DEFAULT_SIZE);
037  }
038
039  /**
040   * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
041   * elements.
042   *
043   * @param distinctElements the expected number of distinct elements
044   * @throws IllegalArgumentException if {@code distinctElements} is negative
045   */
046  public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) {
047    return new HashMultiset<>(distinctElements);
048  }
049
050  /**
051   * Creates a new {@code HashMultiset} containing the specified elements.
052   *
053   * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
054   *
055   * @param elements the elements that the multiset should contain
056   */
057  public static <E extends @Nullable Object> HashMultiset<E> create(
058      Iterable<? extends E> elements) {
059    HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
060    Iterables.addAll(multiset, elements);
061    return multiset;
062  }
063
064  HashMultiset(int distinctElements) {
065    super(distinctElements);
066  }
067
068  @Override
069  ObjectCountHashMap<E> newBackingMap(int distinctElements) {
070    return new ObjectCountHashMap<>(distinctElements);
071  }
072
073  @GwtIncompatible // Not needed in emulated source.
074  @J2ktIncompatible
075  private static final long serialVersionUID = 0;
076}