paintImmediately（）函数没有效果

public class Test extends JFrame {
 JPanel panel = new JPanel();
 int i = 0;

 JButton button = new JButton("da");
     JTextField field1 = new JTextField("aaaa");
     JTextField field2 = new JTextField("bbbb");
     JTextField field3 = new JTextField("cccc");
     public Test(){
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 setBounds(100, 100, 200, 400);
 button.addActionListener(new ac());
 panel.setLayout(new GridLayout(3, 1));
 panel.add(field1);
 panel.add(field2);
 panel.add(field3);
 getContentPane().setLayout(new BorderLayout());
 getContentPane().add(button,BorderLayout.EAST);
 getContentPane().add(panel,BorderLayout.WEST);
     }
     
     public class ac implements ActionListener{


 @Override
 public void actionPerformed(ActionEvent e) {
 // TODO Auto-generated method stub
 updata();
 }
     
     }
     
     public static void main(String[] args){
     Test test = new Test();
     test.setVisible(true);
     
     }
     
     public void updata(){
     try {
     field1.setText(i+1+"");
     field1.paintImmediately(field1.getBounds());
     Thread.sleep(2000);
     
     field2.setText(i+2+"");
     field2.paintImmediately(field2.getBounds());
     Thread.sleep(2000);
     
     field3.setText(i+3+"");
     field3.paintImmediately(field3.getBounds());
     Thread.sleep(2000);
     
     i = i+1;
 } catch (InterruptedException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }
     
     System.out.println("hello");
     }
 }