Add button to unused space in JTableHeader

Question

I have modified my JTable so that I can have multiple rows of column headers. I did this by extending BasicTableHeaderUI. In my particular instance, the first column of the table will never have more than one row in the header (unlike other implementations of multi-row headers I have seen, my column headers don't automatically fill upwards to take up all usable space in the header). So, I have "unused" space in the header above the first column.
I would like to put some buttons there that are relevant to the table, but so far every effort to do so has failed.
In the SSCCE below I have created a very stripped down version of my TableHeaderUI. It doesn't contain any of the code to create multiple row headers, it just pushes down the standard column headers to create some space. I try adding a button to the rendererPane, but it doesn't show up. There is a commented out line that paints the button which does work in terms of showing the button, but that's probably not the right way to do this (and the button doesn't work anyway).
So, why isn't the button showing up? Am I doing this the right way (i.e. adding the button within the UI)? Thanks in advance for you help.
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Enumeration;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.plaf.basic.BasicTableHeaderUI;
import javax.swing.table.TableCellRenderer;
import javax.swing.table.TableColumn;
import javax.swing.table.TableColumnModel;
public class HeaderButtonTable extends JPanel {
     public HeaderButtonTable() {
          String[] colNames = {"column 1", "column2", "column3"};
          Object[][] data = {{"a","b","c"},{"d","e","f"}};
          JTable table = new JTable(data, colNames);
          table.setPreferredScrollableViewportSize(new Dimension(400,100));
          table.setFillsViewportHeight(true);
          table.getTableHeader().setUI(new ButtonHeaderUI());
          JScrollPane scrollPane = new JScrollPane(table);
          add(scrollPane);
     public class ButtonHeaderUI extends BasicTableHeaderUI {
          public void paint(Graphics g, JComponent c) {
               Rectangle clip = g.getClipBounds();
               Point left = clip.getLocation();
               Point right = new Point( clip.x + clip.width - 1, clip.y );
               TableColumnModel cm = header.getColumnModel();
               int cMin = header.columnAtPoint(left);
               int cMax = header.columnAtPoint(right);
               if (cMin == -1) cMin =  0;
               if (cMax == -1) cMax = cm.getColumnCount()-1;
               TableColumn draggedColumn = header.getDraggedColumn();
               int columnWidth;
               Rectangle cellRect = header.getHeaderRect(cMin);
               TableColumn aColumn;
               for(int column = cMin; column <= cMax ; column++) {
                    aColumn = cm.getColumn(column);
                    columnWidth = aColumn.getWidth();
                    cellRect.width = columnWidth;
                    if (aColumn != draggedColumn) {
                         paintCell(g, cellRect, column);
                    cellRect.x += columnWidth;
              JButton test = new JButton("test");
              test.addActionListener(new ActionListener(){
                    public void actionPerformed(ActionEvent e) {
                         System.out.println("pressed");
              test.setBounds(2, 2, 60, 15);
              rendererPane.add(test);  //why isn't this showing up?
              //this line will display the button, but button doesn't work
//          rendererPane.paintComponent(g, test, header, 2, 2, 60, 15);
          private Component getHeaderRenderer(int columnIndex) {
               TableColumn aColumn = header.getColumnModel().getColumn(columnIndex);
               TableCellRenderer renderer = aColumn.getHeaderRenderer();
               if (renderer == null) renderer = header.getDefaultRenderer();
               return renderer.getTableCellRendererComponent(header.getTable(),
                    aColumn.getHeaderValue(), false, false, -1, columnIndex);
          private void paintCell(Graphics g, Rectangle cellRect, int columnIndex) {
               Component component = getHeaderRenderer(columnIndex);
               rendererPane.paintComponent(g, component, header,
                    cellRect.x, cellRect.y + 30, cellRect.width,
                    cellRect.height - 30, true);
          public Dimension getPreferredSize(JComponent c) {
               long width = 0;
               Enumeration enumeration = header.getColumnModel().getColumns();
               while (enumeration.hasMoreElements()) {
                    TableColumn aColumn = (TableColumn)enumeration.nextElement();
                    width = width + aColumn.getPreferredWidth();
               return new Dimension((int)width, 60);
     public static void main(String[] args) {
          JFrame frame = new JFrame();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.add(new HeaderButtonTable());
          frame.pack();
          frame.setVisible(true);
}

Answer 1

Yes, I've seen similar links/posts about how to activate buttons in the header of a table, but those do it by adding listeners to the renderer. My buttons would be directly in the CellRendererPane that is the container for the table header. I would have thought that by putting the button directly in the Cell RendererPane that it would have nothing to do with the rest of the table header. CellRendererPane extends Container. Is it not possible to put a JButton in a Container? JFrame extends indirectly from Container and you can add buttons to that.
Edited by: Bob.B on Oct 28, 2009 10:57 PM