JFrames / JPanels....Am I being stupid here?

Question

I am creating an application for an assignment. I want the button I click to display another screen in the center panel (displayPanel).
But, I get nothing. Nothing displayed, no runtime error, nothing returned on the catch & even if I do a System.out.println() I get nothing in the command prompt.
So, if I am not getting errors etc...where is my display? Any help?
import java.awt.*;
import java.awt.event.*;
import java.awt.Toolkit.*;
import javax.swing.*;
import javax.swing.event.*;
public class Examiner extends JFrame implements ActionListener{
          Screen1 sc=new Screen1();
          StudentScreen ss=new StudentScreen();
          Container content;
          Icon stu_icon=new ImageIcon("../hat.jpeg");
          Icon staff_icon=new ImageIcon("../prof.jpeg");
          Icon course_icon=new ImageIcon("../course.jpeg");
          Icon units_icon=new ImageIcon("../units.jpeg");
          JButton stu=new JButton(stu_icon);
          JButton staff=new JButton(staff_icon);
          JButton course=new JButton(course_icon);
          JButton units=new JButton(units_icon);
          JPanel buttonPanel=new JPanel();
          JPanel menuPanel=new JPanel();
          JPanel displayPanel=new JPanel();
     public Examiner() {
          content=getContentPane();
          content.setLayout(new BorderLayout());
          buttonPanel.setLayout(new GridLayout(6,1));
          buttonPanel.add(stu);
          buttonPanel.add(staff);
          buttonPanel.add(course);
          buttonPanel.add(units);
          content.add("North",menuPanel);
          content.add("West",buttonPanel);
          content.add("Center",displayPanel);          
          addWindowListener(new WindowAdapter() {
               public void windowClosing(WindowEvent e) {
                    dispose();
                    System.exit(0);
     }// end examiner() constructor
          public void actionPerformed(ActionEvent clicked){
          if(clicked.getSource()==stu){
               try{
               test();
          catch(Exception e){e.printStackTrace();
          }// end if
     }//end actionperformed
          public void paint(Graphics g){
               this.paintComponents(g);      
               super.paint(g);
     }//end paint
     public void test(){
          displayPanel.add(units);
     public static void main(String args[]) {
          Examiner mainFrame = new Examiner();
          mainFrame.setSize(mainFrame.getToolkit().getScreenSize());
          mainFrame.setTitle("Examiner");
          mainFrame.setVisible(true);
     }// end main
}//end Examiner classI have tried to get this to work by calling it from another class (StudentScreen) and also as shown above by simply trying to get it to display one of the icons again. Could use some pointers here
Thanks

Answer 1

<<<< falls over>>>>
Now I am really embarrassed. I should have seen that a long time ago. Guess I need to take a break lol
thanks very much for the help.