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Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0

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/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.util.HashMap;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Multiset implementation backed by a {@link HashMap}.
 *
 * @author Kevin Bourrillion
 */
public final class HashMultiset extends AbstractMapBasedMultiset {
  /**
   * Constructs a new empty {@code HashMultiset} using the default initial
   * capacity (16 distinct elements) and load factor (0.75).
   */
  public HashMultiset() {
    super(new HashMap());
  }

  /**
   * Constructs a new empty {@code HashMultiset} with the specified expected
   * number of distinct elements and the default load factor (0.75).
   *
   * @param distinctElements the expected number of distinct elements
   * @throws IllegalArgumentException if {@code distinctElements} is negative
   */
  public HashMultiset(int distinctElements) {
    super(new HashMap(Maps.capacity(distinctElements)));
  }

  /**
   * Constructs a new empty {@code HashMultiset} using the specified initial
   * capacity (distinct elements) and load factor.
   *
   * @param initialCapacity the initial capacity
   * @param loadFactor the load factor
   * @throws IllegalArgumentException if the initial capacity is negative
   */
  public HashMultiset(int initialCapacity, float loadFactor) {
    super(new HashMap(initialCapacity, loadFactor));
  }

  /**
   * Constructs a new {@code HashMultiset} containing the specified elements.
   *
   * @param elements the elements that the multiset should contain
   */
  public HashMultiset(Iterable elements) {
    this(Multisets.inferDistinctElements(elements));
    Iterables.addAll(this, elements); // careful if we make this class non-final
  }

  private static final long serialVersionUID = 2422072640108355431L;
}