001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.multiset;
018
019import java.io.IOException;
020import java.io.ObjectInputStream;
021import java.io.ObjectOutputStream;
022import java.io.Serializable;
023import java.util.Collection;
024import java.util.HashMap;
025
026/**
027 * Implements {@code MultiSet}, using a {@link HashMap} to provide the
028 * data storage. This is the standard implementation of a multiset.
029 * <p>
030 * A {@code MultiSet} stores each object in the collection together with a
031 * count of occurrences. Extra methods on the interface allow multiple copies
032 * of an object to be added or removed at once.
033 *
034 * @param <E> the type held in the multiset
035 * @since 4.1
036 */
037public class HashMultiSet<E> extends AbstractMapMultiSet<E> implements Serializable {
038
039    /** Serial version lock */
040    private static final long serialVersionUID = 20150610L;
041
042    /**
043     * Constructs an empty {@link HashMultiSet}.
044     */
045    public HashMultiSet() {
046        super(new HashMap<E, MutableInteger>());
047    }
048
049    /**
050     * Constructs a multiset containing all the members of the given collection.
051     *
052     * @param coll  a collection to copy into this multiset
053     */
054    public HashMultiSet(final Collection<? extends E> coll) {
055        this();
056        addAll(coll);
057    }
058
059    //-----------------------------------------------------------------------
060    /**
061     * Write the multiset out using a custom routine.
062     *
063     * @param out  the output stream
064     * @throws IOException if an error occurs while writing to the stream
065     */
066    private void writeObject(final ObjectOutputStream out) throws IOException {
067        out.defaultWriteObject();
068        super.doWriteObject(out);
069    }
070
071    /**
072     * Read the multiset in using a custom routine.
073     *
074     * @param in the input stream
075     * @throws IOException if an error occurs while reading from the stream
076     * @throws ClassNotFoundException if an object read from the stream can not be loaded
077     */
078    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
079        in.defaultReadObject();
080        setMap(new HashMap<E, MutableInteger>());
081        super.doReadObject(in);
082    }
083
084}