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.Comparator;
025    import java.util.SortedMap;
026    import java.util.TreeMap;
027    
028    import org.apache.commons.collections.SortedBag;
029    
030    /**
031     * Implements <code>SortedBag</code>, using a <code>TreeMap</code> to provide
032     * the data storage. This is the standard implementation of a sorted bag.
033     * <p>
034     * Order will be maintained among the bag members and can be viewed through the
035     * iterator.
036     * <p>
037     * A <code>Bag</code> stores each object in the collection together with a
038     * count of occurrences. Extra methods on the interface allow multiple copies
039     * of an object to be added or removed at once. It is important to read the
040     * interface javadoc carefully as several methods violate the
041     * <code>Collection</code> interface specification.
042     *
043     * @since Commons Collections 3.0 (previously in main package v2.0)
044     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
045     * 
046     * @author Chuck Burdick
047     * @author Stephen Colebourne
048     */
049    public class TreeBag
050            extends AbstractMapBag implements SortedBag, Serializable {
051    
052        /** Serial version lock */
053        private static final long serialVersionUID = -7740146511091606676L;
054        
055        /**
056         * Constructs an empty <code>TreeBag</code>.
057         */
058        public TreeBag() {
059            super(new TreeMap());
060        }
061    
062        /**
063         * Constructs an empty bag that maintains order on its unique
064         * representative members according to the given {@link Comparator}.
065         * 
066         * @param comparator  the comparator to use
067         */
068        public TreeBag(Comparator comparator) {
069            super(new TreeMap(comparator));
070        }
071    
072        /**
073         * Constructs a <code>TreeBag</code> containing all the members of the
074         * specified collection.
075         * 
076         * @param coll  the collection to copy into the bag
077         */
078        public TreeBag(Collection coll) {
079            this();
080            addAll(coll);
081        }
082    
083        //-----------------------------------------------------------------------
084        public Object first() {
085            return ((SortedMap) getMap()).firstKey();
086        }
087    
088        public Object last() {
089            return ((SortedMap) getMap()).lastKey();
090        }
091    
092        public Comparator comparator() {
093            return ((SortedMap) getMap()).comparator();
094        }
095    
096        //-----------------------------------------------------------------------
097        /**
098         * Write the bag out using a custom routine.
099         */
100        private void writeObject(ObjectOutputStream out) throws IOException {
101            out.defaultWriteObject();
102            out.writeObject(comparator());
103            super.doWriteObject(out);
104        }
105    
106        /**
107         * Read the bag in using a custom routine.
108         */
109        private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
110            in.defaultReadObject();
111            Comparator comp = (Comparator) in.readObject();
112            super.doReadObject(new TreeMap(comp), in);
113        }
114        
115    }