    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 * </p>
    034 *
    035 * @param <E> the type held in the multiset
    036 * @since 4.1
    037 */
    038public class HashMultiSet<E> extends AbstractMapMultiSet<E> implements Serializable {
    039
    040    /** Serial version lock */
    041    private static final long serialVersionUID = 20150610L;
    042
    043    /**
    044     * Constructs an empty {@link HashMultiSet}.
    045     */
    046    public HashMultiSet() {
    047        super(new HashMap<>());
    048    }
    049
    050    /**
    051     * Constructs a multiset containing all the members of the given collection.
    052     *
    053     * @param coll  a collection to copy into this multiset
    054     */
    055    public HashMultiSet(final Collection<? extends E> coll) {
    056        this();
    057        addAll(coll);
    058    }
    059
    060    /**
    061     * Deserializes the multiset in using a custom routine.
    062     *
    063     * @param in the input stream
    064     * @throws IOException if an error occurs while reading from the stream
    065     * @throws ClassNotFoundException if an object read from the stream cannot be loaded
    066     */
    067    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    068        in.defaultReadObject();
    069        setMap(new HashMap<>());
    070        super.doReadObject(in);
    071    }
    072
    073    /**
    074     * Serializes this object to an ObjectOutputStream.
    075     *
    076     * @param out the target ObjectOutputStream.
    077     * @throws IOException thrown when an I/O errors occur writing to the target stream.
    078     */
    079    private void writeObject(final ObjectOutputStream out) throws IOException {
    080        out.defaultWriteObject();
    081        super.doWriteObject(out);
    082    }
    083
    084}