001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry.contrib.table.model.simple;
016    
017    import java.util.Comparator;
018    
019    /**
020     * In order to provide more generic behaviour, ITableColumn has no "column
021     * value" concept. The comparator it returns compares two table rows, rather
022     * than values specific to the column.
023     * <p>
024     * SimpleTableColumn introduces the concept of "column value" and allows one to
025     * extract that "column value" from the row using the getColumnValue() method.
026     * In practice comparisons are also typically done between these values rather
027     * than the full row objects.
028     * <p>
029     * This comparator extracts the column values from the rows passed and uses the
030     * provided comparator to compare the values. It therefore allows a comparator
031     * designed for comparing column values to be quickly wrapped and used as a
032     * comparator comparing rows, which is what ITableColumn is expected to return.
033     * <p>
034     * Example:
035     * <p>
036     * objColumn.setComparator(new ColumnComparator(objColumn, objBeanComparator));
037     * 
038     * @author mindbridge
039     */
040    public class ColumnComparator implements Comparator
041    {
042    
043        private SimpleTableColumn m_objColumn;
044        private Comparator m_objComparator;
045    
046        public ColumnComparator(SimpleTableColumn objColumn,
047                Comparator objComparator)
048        {
049            m_objColumn = objColumn;
050            m_objComparator = objComparator;
051        }
052    
053        /**
054         * @see java.util.Comparator#compare(Object, Object)
055         */
056        public int compare(Object objRow1, Object objRow2)
057        {
058            Object objValue1 = m_objColumn.getColumnValue(objRow1);
059            Object objValue2 = m_objColumn.getColumnValue(objRow2);
060    
061            return m_objComparator.compare(objValue1, objValue2);
062        }
063    
064    }