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     */
017    package org.apache.commons.collections.bag;
018    
019    import java.io.IOException;
020    import java.io.ObjectInputStream;
021    import java.io.ObjectOutputStream;
022    import java.io.Serializable;
023    import java.util.Collection;
024    import java.util.HashMap;
025    
026    import org.apache.commons.collections.Bag;
027    
028    /**
029     * Implements <code>Bag</code>, using a <code>HashMap</code> to provide the
030     * data storage. This is the standard implementation of a bag.
031     * <p>
032     * A <code>Bag</code> stores each object in the collection together with a
033     * count of occurrences. Extra methods on the interface allow multiple copies
034     * of an object to be added or removed at once. It is important to read the
035     * interface javadoc carefully as several methods violate the
036     * <code>Collection</code> interface specification.
037     *
038     * @since Commons Collections 3.0 (previously in main package v2.0)
039     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
040     * 
041     * @author Chuck Burdick
042     * @author Stephen Colebourne
043     */
044    public class HashBag
045            extends AbstractMapBag implements Bag, Serializable {
046    
047        /** Serial version lock */
048        private static final long serialVersionUID = -6561115435802554013L;
049        
050        /**
051         * Constructs an empty <code>HashBag</code>.
052         */
053        public HashBag() {
054            super(new HashMap());
055        }
056    
057        /**
058         * Constructs a bag containing all the members of the given collection.
059         * 
060         * @param coll  a collection to copy into this bag
061         */
062        public HashBag(Collection coll) {
063            this();
064            addAll(coll);
065        }
066    
067        //-----------------------------------------------------------------------
068        /**
069         * Write the bag out using a custom routine.
070         */
071        private void writeObject(ObjectOutputStream out) throws IOException {
072            out.defaultWriteObject();
073            super.doWriteObject(out);
074        }
075    
076        /**
077         * Read the bag in using a custom routine.
078         */
079        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
080            in.defaultReadObject();
081            super.doReadObject(new HashMap(), in);
082        }
083        
084    }