    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.bag;
    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 Bag}, using a {@link HashMap} to provide the
    028 * data storage. This is the standard implementation of a bag.
    029 * <p>
    030 * A {@code Bag} 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. It is important to read the
    033 * interface javadoc carefully as several methods violate the
    034 * {@link Collection} interface specification.
    035 * </p>
    036 *
    037 * @param <E> the type of elements in this bag
    038 * @since 3.0 (previously in main package v2.0)
    039 */
    040public class HashBag<E> extends AbstractMapBag<E> implements Serializable {
    041
    042    /** Serial version lock */
    043    private static final long serialVersionUID = -6561115435802554013L;
    044
    045    /**
    046     * Constructs an empty {@link HashBag}.
    047     */
    048    public HashBag() {
    049        super(new HashMap<E, MutableInteger>());
    050    }
    051
    052    /**
    053     * Constructs a bag containing all the members of the given collection.
    054     *
    055     * @param coll  a collection to copy into this bag
    056     */
    057    public HashBag(final Collection<? extends E> coll) {
    058        this();
    059        addAll(coll);
    060    }
    061
    062    //-----------------------------------------------------------------------
    063    /**
    064     * Write the bag out using a custom routine.
    065     *
    066     * @param out  the output stream
    067     * @throws IOException if an error occurs while writing to the stream
    068     */
    069    private void writeObject(final ObjectOutputStream out) throws IOException {
    070        out.defaultWriteObject();
    071        super.doWriteObject(out);
    072    }
    073
    074    /**
    075     * Read the bag in using a custom routine.
    076     *
    077     * @param in  the input stream
    078     * @throws IOException if an error occurs while reading from the stream
    079     * @throws ClassNotFoundException if an object read from the stream can not be loaded
    080     */
    081    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    082        in.defaultReadObject();
    083        super.doReadObject(new HashMap<E, MutableInteger>(), in);
    084    }
    085
    086}