    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}