CheckBox in Column of JTable: Exception: java.lang.String cannot be cast to java.lang.Boolean

Hello, I have discovered a hidden error. My project was working for awhile, but then I started to get the below error.

My error comes from the fact that I'm using a checkbox in a jtable, and I'm using the below "getColumnClass".

Thank you,

compile:
run:
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Boolean
    at javax.swing.JTable$BooleanRenderer.getTableCellRendererComponent(JTable.java:5412)
    at javax.swing.JTable.prepareRenderer(JTable.java:5735)
    at javax.swing.plaf.basic.BasicTableUI.paintCell(BasicTableUI.java:2114)
    at javax.swing.plaf.basic.BasicTableUI.paintCells(BasicTableUI.java:2016)
    at javax.swing.plaf.basic.BasicTableUI.paint(BasicTableUI.java:1812)
    at javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
    at javax.swing.JComponent.paintComponent(JComponent.java:778)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1482)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1413)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
    at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:701)
    at java.awt.EventQueue.access$000(EventQueue.java:102)
    at java.awt.EventQueue$3.run(EventQueue.java:662)
    at java.awt.EventQueue$3.run(EventQueue.java:660)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:671)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

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The below project runs perfectly. Without seeing my large project, how can I modify the below project to get my other large project to work.

package sorttable;

import javax.swing.*;
   import javax.swing.table.*;
   import java.awt.*;
import java.util.ArrayList;

   public class SortTable {
     public static void main(String args[]) {
       Runnable runner = new Runnable() {
        public void run() {
           JFrame frame = new JFrame("Sorting JTable");
           frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           Object rows[][] = {
               {"VOD", "Vodafone Group", 26.02, new Boolean(false), new Boolean(false)},
               {"SUNW", "Sun Microsystems", 3.86, new Boolean(true), new Boolean(false)},
               {"EBAY", "eBay", 41.57, new Boolean(false), new Boolean(false)},
               {"GOOG", "Google", 388.33, new Boolean(false), new Boolean(false)},
               {"MSFT", "Microsoft", 26.56, new Boolean(true), new Boolean(false)},
               {"NOK", "Nokia Corp", 17.13, new Boolean(false), new Boolean(false)},
               {"ORCL", "Oracle Corp.", 12.52, new Boolean(true), new Boolean(false)},
               {"TWX", "Time Warner", 17.66, new Boolean(false), new Boolean(false)},
               {"AMZN", "Amazon", 41.28, new Boolean(false), new Boolean(false)},
               {"YHOO", "Yahoo!", 37.69, new Boolean(false), new Boolean(false)}
             };
           String columns[] = {"Symbol", "Name", "Price", "OK", "Cheap"};
           TableModel model =
               new DefaultTableModel(rows, columns) {
             public Class getColumnClass(int column) {
               Class returnValue;
               if ((column >= 0) && (column < getColumnCount())) {
                 returnValue = getValueAt(0, column).getClass();
               } else {
                 returnValue = Object.class;
               }
               return returnValue;
             }
           };

           JTable table = new JTable(model);
           RowSorter<TableModel> sorter =
             new TableRowSorter<TableModel>(model);
           
           java.util.List sortKeys = new ArrayList();
           sortKeys.add(new RowSorter.SortKey(3, SortOrder.ASCENDING));
           sorter.setSortKeys(sortKeys);

           table.setRowSorter(sorter);
           JScrollPane pane = new JScrollPane(table);
           frame.add(pane, BorderLayout.CENTER);
           frame.setSize(300, 150);
           frame.setVisible(true);
         }
       };
       EventQueue.invokeLater(runner);
     }
   }