oldViewport.addChangeListener(viewportChangeListener);
newViewport.addChangeListener(viewportChangeListener); syncScrollPaneWithViewport();
  protected void updateViewport(PropertyChangeEvent ev)  {    JViewport oldViewport = (JViewport) ev.getOldValue();    oldViewport.removeChangeListener(viewportChangeListener);    JViewport newViewport = (JViewport) ev.getNewValue();    oldViewport.addChangeListener(viewportChangeListener);  }