Decorator for JTable

Question

Hi!
I'd like to have a Decorator for a JTable drawing a complete grid in the Viewport, not only of the size of the table.
The code I wrote:
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JViewport;
import javax.swing.UIManager;
public class ScrollPaneDecorator extends JComponent {
     private static final long serialVersionUID = 1155581978481349791L;
     protected JScrollPane child;
     protected JTable table;
     public ScrollPaneDecorator(JScrollPane child) {
          this.child = child;
          Component[] viewportComps = child.getViewport().getComponents();
          for (Component comp : viewportComps) {
               if (comp instanceof JTable) {
                    this.table = (JTable)comp;
          this.setLayout(new BorderLayout());
          this.add(child);
     public void paint(Graphics g) {
          super.paint(g);
          g.setColor( UIManager.getColor("Table.gridColor") );
          int y = table.getRowHeight(0);
          Double visibleHeight = new Double(0);
          Double scrollPaneWidth = new Double(0);
          if (table.getParent() instanceof JViewport) {
               JViewport viewPort = ((JViewport)table.getParent());
               scrollPaneWidth = viewPort.getVisibleRect().getWidth();
               visibleHeight = viewPort.getVisibleRect().getHeight();
          int i=1;
          while (y*i<visibleHeight) {
               g.drawLine(0, y*i-2, scrollPaneWidth.intValue(), y*i-2);
               i++;
          int columnCount = table.getColumnCount();
          int x = 0;
          for (int j=0; j<columnCount; j++) {
               x += table.getColumnModel().getColumn(j).getWidth();
               g.drawLine(x, y, x, visibleHeight.intValue());
}This works quiet nice. The only Problem is, that the Viewport doesn't repaint, when the Table-Data changes.
I also tried to write a Decorator directly for the table. But when I used it, the table showed up without the tableHeaders.
Has anyone tried something similar? Thanks for any hint!

Answer 1

First of all, it's not really a decorator pattern. You should override and delegate every public and protected method in JComponent for that.
Also, you would typically override the method paintComponent() instead of paint(). That could be the main problem.