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 
021     * has no "column value" concept. The comparator it returns 
022     * compares two table rows, rather than values specific to the column. 
023     * <p>
024     * SimpleTableColumn introduces the concept of "column value" and 
025     * allows one to extract that "column value" from the row using 
026     * the getColumnValue() method. In practice comparisons are also typically 
027     * done between these values rather than the full row objects.
028     * <p>
029     * This comparator extracts the column values from the rows passed 
030     * and uses the provided comparator to compare the values.
031     * It therefore allows a comparator designed for comparing column values to be
032     * quickly wrapped and used as a comparator comparing rows, which is what
033     * ITableColumn is expected to return.
034     * <p>
035     * Example:
036     * <p>
037     * objColumn.setComparator(new ColumnComparator(objColumn, objBeanComparator));    
038     * 
039     * @author mindbridge
040     *
041     */
042    public class ColumnComparator implements Comparator
043    {
044        private SimpleTableColumn m_objColumn;
045            private Comparator m_objComparator;
046    
047            public ColumnComparator(SimpleTableColumn objColumn, 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    }