Java applet in dialogbox, can't refresh applet UI

notes/domino 8.0.1a very simple applet(see below), use a dialog box to show it, but when I move this dialog box, applet can’t refresh . I try to use repaint,but it doesn’t work, so suggestion will be appreciated.

package test;

import javax.swing.*;

import lotus.domino.JAppletBase;

public class GlassPaneDemo extends JAppletBase{

public void notesAppletInit()

{ 

	try {

	        javax.swing.SwingUtilities.invokeAndWait(new Runnable() {

	            public void run() {

	            	createUI();

	            }

	        });

	    } catch (Exception e) {

	        System.err.println("createGUI didn't successfully complete");

	    }    	

}   





private void createUI(){    	

	JButton btnTest = new JButton();

	btnTest.setText("test button");		

	btnTest.addActionListener(new java.awt.event.ActionListener() {

            public void actionPerformed(java.awt.event.ActionEvent evt) {

            	System.out.println("test clicked !!");

            }

        });

	 

	this.getContentPane().add(btnTest);

     setVisible(true);	     

}



public void notesAppletStart()

{        

    this.setVisible(true);

    System.out.println("notes applet start");        

}

}