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 java.io.IOException; 023import java.io.ObjectInputStream; 024import java.io.ObjectOutputStream; 025import java.util.HashMap; 026import org.checkerframework.checker.nullness.qual.Nullable; 027 028/** 029 * Multiset implementation backed by a {@link HashMap}. 030 * 031 * @author Kevin Bourrillion 032 * @author Jared Levy 033 * @since 2.0 034 */ 035@GwtCompatible(serializable = true, emulated = true) 036@ElementTypesAreNonnullByDefault 037public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> { 038 039 /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */ 040 public static <E extends @Nullable Object> HashMultiset<E> create() { 041 return new HashMultiset<E>(); 042 } 043 044 /** 045 * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct 046 * elements. 047 * 048 * @param distinctElements the expected number of distinct elements 049 * @throws IllegalArgumentException if {@code distinctElements} is negative 050 */ 051 public static <E extends @Nullable Object> HashMultiset<E> create(int distinctElements) { 052 return new HashMultiset<E>(distinctElements); 053 } 054 055 /** 056 * Creates a new {@code HashMultiset} containing the specified elements. 057 * 058 * <p>This implementation is highly efficient when {@code elements} is itself a {@link Multiset}. 059 * 060 * @param elements the elements that the multiset should contain 061 */ 062 public static <E extends @Nullable Object> HashMultiset<E> create( 063 Iterable<? extends E> elements) { 064 HashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements)); 065 Iterables.addAll(multiset, elements); 066 return multiset; 067 } 068 069 private HashMultiset() { 070 super(new HashMap<E, Count>()); 071 } 072 073 private HashMultiset(int distinctElements) { 074 super(Maps.<E, Count>newHashMapWithExpectedSize(distinctElements)); 075 } 076 077 /** 078 * @serialData the number of distinct elements, the first element, its count, the second element, 079 * its count, and so on 080 */ 081 @GwtIncompatible // java.io.ObjectOutputStream 082 @J2ktIncompatible 083 private void writeObject(ObjectOutputStream stream) throws IOException { 084 stream.defaultWriteObject(); 085 Serialization.writeMultiset(this, stream); 086 } 087 088 @GwtIncompatible // java.io.ObjectInputStream 089 @J2ktIncompatible 090 private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException { 091 stream.defaultReadObject(); 092 int distinctElements = Serialization.readCount(stream); 093 setBackingMap(Maps.<E, Count>newHashMap()); 094 Serialization.populateMultiset(this, stream, distinctElements); 095 } 096 097 @GwtIncompatible // Not needed in emulated source. 098 @J2ktIncompatible 099 private static final long serialVersionUID = 0; 100}