从未调用过JTable TableCellRenderer getTableCellRendererComponent（）

Question

I am trying to implement a JTable which will format cells in columns in ways depending on their type. I am implementing TableCellRenderer's `getTableCellRendererComponent()' method to achieve this.

The problem is that my getTableCellRendererComponent() method never seems to be called, as the test output in the code never appears in the console.

Here is the code for the renderer:

public class MenuSheetTableCellRenderer extends JLabel implements TableCellRenderer {

@Override
public Component getTableCellRendererComponent(
                        JTable table, Object value,
                        boolean isSelected, boolean hasFocus,
                        int row, int column){

JLabel label = new JLabel();

System.out.println("test");
if( value instanceof GregorianCalendar ){
    System.out.println("test2");
    GregorianCalendar timeGregorianCalendar = (GregorianCalendar) value;
    Date time = timeGregorianCalendar.getTime();
    SimpleDateFormat timeFormat = new SimpleDateFormat("hh:mm a");
    String mealTime = timeFormat.format(time);

    label.setText(mealTime);
}

else if( value instanceof MealChoice){
    label.setText(value.toString());
}   
else if( value instanceof Recipe){
    label.setText("     " + value.toString());
}
if (value instanceof String || value instanceof MealChoice){
    label.setFont(new Font("Tahoma", Font.BOLD, 11));
}

return label;
}

}

Here is the code (edited for relevant code) which generates the table. Note that getRows() is my custom method that returns the data to be rendered and also that I am using netbeans (hence the abridged initComponents() method). Should be irrelevant.

private void initComponents() {
menuSheetTable = new javax.swing.JTable();
menuSheetTable.setModel(new javax.swing.table.DefaultTableModel(
        new Object [][] {

        },
        new String [] {

        }
    ));
    menuSheetTable.setEnabled(false);
    menuSheetTable.setFocusable(false);
    menuSheetTable.setShowHorizontalLines(false);
    menuSheetTable.setShowVerticalLines(false);
    jScrollPane1.setViewportView(menuSheetTable);
}

public void renderTable(){

String[] columns = { "Sunday", "Monday","Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; 
Object[][] rows = getRows();

DefaultTableModel menuSheetModel = new DefaultTableModel( rows, columns );
menuSheetTable.setModel( menuSheetModel );

MenuSheetTableCellRenderer renderer = new MenuSheetTableCellRenderer();
try{
   menuSheetTable.setDefaultRenderer(Class.forName("java.lang.String"), renderer);
   menuSheetTable.setDefaultRenderer(Class.forName("java.util.GregorianCalendar"), renderer); 
   menuSheetTable.setDefaultRenderer(Class.forName("MenuSystemManager.MealChoice"), renderer);
   menuSheetTable.setDefaultRenderer(Class.forName("MenuSystemManager.Recipe"), renderer);
}
catch( ClassNotFoundException e){
    System.exit(1);
}
}

Answer 1

The code which set the default renderers doesn't have the Object object registered. Because the rows[][] was declared to hold type "Object," the renderer was never called because it was passed Object objects, not GregorianCalendar s, String s, or Recipe s.

Answer 2

I ran into the same issue. Well, you have already found the reason why it behaves like this. So, here is the solution.

JTable works with TableModel interface that supplies table with all information about the data it holds. This information also contains the class associated with a column. So basically, what you need to do is to derive TableModel or AbstractTableModel with your class which will hold the data for the table and override the method public Class<?> getColumnClass(int columnIndex) . After that enhancement you can use your custom TableCellRenderer . In your code you supplied JTable with a DefaultTableModel which returns Object for any column and that's why it did not work out.