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<>());
050    }
051
052    /**
053     * Constructs a bag containing all the members of the given Collection.
054     *
055     * @param collection a collection to copy into this bag.
056     */
057    public HashBag(final Collection<? extends E> collection) {
058        this();
059        addAll(collection);
060    }
061
062    /**
063     * Constructs a bag containing all the members of the given Iterable.
064     *
065     * @param iterable an iterable to copy into this bag.
066     * @since 4.5.0-M3
067     */
068    public HashBag(final Iterable<? extends E> iterable) {
069        super(new HashMap<>(), iterable);
070    }
071
072    /**
073     * Deserializes the bag in using a custom routine.
074     *
075     * @param in  the input stream
076     * @throws IOException if an error occurs while reading from the stream
077     * @throws ClassNotFoundException if an object read from the stream cannot be loaded
078     */
079    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
080        in.defaultReadObject();
081        super.doReadObject(new HashMap<>(), in);
082    }
083
084    /**
085     * Serializes this object to an ObjectOutputStream.
086     *
087     * @param out the target ObjectOutputStream.
088     * @throws IOException thrown when an I/O errors occur writing to the target stream.
089     */
090    private void writeObject(final ObjectOutputStream out) throws IOException {
091        out.defaultWriteObject();
092        super.doWriteObject(out);
093    }
094
095}