paintImmediately（）函数没有效果? 400 报错

paintImmediately（）函数没有效果? 400 报错

@Kooosy 你好，想跟你请教个问题：

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");
    }
}


例如这个程序，只有field1会立刻更新，field2、field3都是等主程序完成才更新，为什么呢