Interface Not Updating Properly

The program runs well , it adds the applet but it dosn't update the interface unless I press "_"(Minimize) . To be more clear , the object paints a spring wich goes through 4 stages , it is added to the JFrame but it dosn't uptade until I minimize the frame , that is when it goes to the next stage .

The main class which calls the spring to be added to the frame :

public class principal implements ActionListener ,Runnable{
JTextField field;
JFrame frame;
private class Action implements ActionListener {
public void actionPerformed(ActionEvent event) {
  frame.repaint();

[Code] .....