Custom Border painting over scrollpane and toolbar

Question

I found a LineNumberBorder class in these here forums (I'll post this same question there too) and adapted it to add line numbers to a JTextPane derived class.
When the border is added to the textpane it paints line numbers to the left of each line in the editor.
When this composite (textpane and border) is added to a tabbedpane, all is well, unless I switch to another window. When I come back to the editor, the line numbers are being painted beyond the top and/or bottom of the jscrollpane.
package com.marklawford.editor.textpane;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.text.*;
* LineNumberBorder.java
* Created: Wed Aug 25 22:15:12 1999
* @author Sandip Chitale ([email protected])
* Copyright 1999. All rights reserved.
* originally handled text area components
* adapted by Mark Lawford to accept SyntaxedEditor components which extend JTextPane
* the getLineStartOffset(int i) method had to be implemented in SyntaxedEditor
* the int getLineCount() method had to be implemented in SyntaxedEditor
public class LineNumberBorder extends AbstractBorder {
private Color numberColor;
     public LineNumberBorder() {
     public LineNumberBorder(Color lineNumberColor) {
          numberColor = lineNumberColor;
     * Paints the border for the specified component with the specified
     * position and size.
     * @param c the component for which this border is being painted
     * @param g the paint graphics
     * @param x the x position of the painted border
     * @param y the y position of the painted border
     * @param width the width of the painted border
     * @param height the height of the painted border
     public void paintBorder(Component c, Graphics g, int x, int y, int width, int height){
          if (!(c instanceof SyntaxedEditor)) {
               return;
          Insets insets = getBorderInsets(c);
          Color oldColor = g.getColor();
          if (numberColor == null) numberColor = c.getForeground();
          g.setColor(numberColor);
          g.translate(x, y);
          SyntaxedEditor ta = (SyntaxedEditor) c;
     // Mask the left margin area
          Graphics cg = g.create();
          cg.setClip(0, insets.top, insets.left, height - insets.top);
          Font f = ta.getFont();
          FontMetrics fm = cg.getFontMetrics(f);
          int lines = ta.getLineCount();
          for (int i = 0; i < lines; i++) {
               try {
                    Rectangle r = ta.modelToView(ta.getLineStartOffset(i));
                    int lx = insets.left - fm.stringWidth("W" + (i+1));
                    int ly = r.y + fm.getLeading() + fm.getMaxAscent();
                    //draw the line number (as a string) at the coordinates provided
//how can I tell whether ly is outside of the viewable area?
                    cg.drawString("" + (i+1), lx, ly);
               } catch (BadLocationException ble) {
          cg.dispose();
          g.setColor(oldColor);
     * Returns the insets of the border.
     * @param c the component for which this border insets value applies
     public Insets getBorderInsets(Component c){
          if (!(c instanceof SyntaxedEditor)) {
               return new Insets(0,0,0,0);
          FontMetrics fm = c.getFontMetrics(c.getFont());
          //int margin = fm.stringWidth("WWWW");
          int margin = fm.stringWidth( new String("W"+((SyntaxedEditor)c).getLineCount()) );
          return new Insets(0,margin,0,0);
     * Returns whether or not the border is opaque. If the border
     * is opaque, it is responsible for filling in it's own
     * background when painting.
     public boolean isBorderOpaque(){
          return false;
     public static void main(String args[]){
          JFrame jf = new JFrame();
          Container cp = jf.getContentPane();
          cp.setLayout(new BorderLayout());
          SyntaxedEditor ta = new SyntaxedEditor();
          //all we need to do is this...
          ta.setBorder( new LineNumberBorder(Color.red) );
          //ta.setLineWrap(true);
          cp.add(new JScrollPane(ta), BorderLayout.CENTER);
          jf.setSize(300, 400);
          jf.setVisible(true);
          jf.addWindowListener(new WindowAdapter() {
          public void windowActivated(WindowEvent e) {}
          public void windowClosed(WindowEvent e) {}
          public void windowClosing(WindowEvent e) {System.exit(0);}
          public void windowDeactivated(WindowEvent e) {}
          public void windowDeiconified(WindowEvent e) {}
          public void windowIconified(WindowEvent e) {}
          public void windowOpened(WindowEvent e) {}});
} // LineNumberBorder

Answer 1

The LineNumberBorder just extends AbstractBorder which extends Object, so there can't be any issues about mixing heavy weight and light weight components... can there?
I'm stumped. The border is painting all the line numbers, as I would expect from the code, but the Scrollpane isn't hiding them. The numbers paint right on top of surrounding components until some action on my part causes those comps to explicitly repaint themselves.
Any ideas? Anyone?