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