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.comparators;
018    
019    import java.util.Comparator;
020    
021    import org.apache.commons.collections.Transformer;
022    
023    /**
024     * Decorates another Comparator with transformation behavior. That is, the
025     * return value from the transform operation will be passed to the decorated
026     * {@link Comparator#compare(Object,Object) compare} method.
027     * 
028     * @since Commons Collections 2.0 (?)
029     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
030     * 
031     * @see org.apache.commons.collections.Transformer
032     * @see org.apache.commons.collections.comparators.ComparableComparator
033     */
034    public class TransformingComparator implements Comparator {
035        
036        /** The decorated comparator. */
037        protected Comparator decorated;
038        /** The transformer being used. */    
039        protected Transformer transformer;
040    
041        //-----------------------------------------------------------------------
042        /**
043         * Constructs an instance with the given Transformer and a 
044         * {@link ComparableComparator ComparableComparator}.
045         * 
046         * @param transformer what will transform the arguments to <code>compare</code>
047         */
048        public TransformingComparator(Transformer transformer) {
049            this(transformer, new ComparableComparator());
050        }
051    
052        /**
053         * Constructs an instance with the given Transformer and Comparator.
054         * 
055         * @param transformer  what will transform the arguments to <code>compare</code>
056         * @param decorated  the decorated Comparator
057         */
058        public TransformingComparator(Transformer transformer, Comparator decorated) {
059            this.decorated = decorated;
060            this.transformer = transformer;
061        }
062    
063        //-----------------------------------------------------------------------
064        /**
065         * Returns the result of comparing the values from the transform operation.
066         * 
067         * @param obj1  the first object to transform then compare
068         * @param obj2  the second object to transform then compare
069         * @return negative if obj1 is less, positive if greater, zero if equal
070         */
071        public int compare(Object obj1, Object obj2) {
072            Object value1 = this.transformer.transform(obj1);
073            Object value2 = this.transformer.transform(obj2);
074            return this.decorated.compare(value1, value2);
075        }
076    
077    }
078