JPanel可见性（true）未显示

Question

我有一个主机和一个带有计时器的strartscreen从3,2,1倒计时。 我已经设置了主机main.setVisible（false）但是当计时器达到0时我希望它是main.setVisible（true）。我做了这个，但它似乎没有工作，我不知道我做错了什么。这是我到目前为止： *大型机：

public class MainPanel extends JPanel {

public JLabel welkom, vraag, vraagnr, minimize, close;
public JButton btnVolgende, btnExit, btnVraag;
public ImageIcon icon;

public MainPanel() {
    setLayout(null);
    setVisible(false); // visibility false

Timerframe：

MainPanel main = new MainPanel();
    Vraag1 vraag1 = new Vraag1();


    ActionListener listener = new ActionListener() 
    {
        int seconden = 3;
        public void actionPerformed(ActionEvent e) {
            seconden--;
            if(seconden > 0)
            {
                countdown.setText("" + seconden);
            }
            else if(seconden == 0)
            {
                main.setVisible(true); //setframe visible
                vraag1.setVisible(true);
                setVisible(false);
            }
        }

    };
    afteller = new Timer(1000, listener);
    afteller.start();

}

这是我的JFrame：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseListener;

import javax.swing.ImageIcon;
import javax.swing.JFrame;

import com.sun.glass.events.MouseEvent;

public class Frame {

    static JFrame frame;
    static MainPanel paneel;
    static Vraag1 vraag1;
    static StartScherm start;

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        frame = new JFrame();
        frame.setLayout(null);
        frame.setTitle("Voetbal quiz - Edward Kerckhof");
        frame.setSize(1191,677);    
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        ImageIcon icon = new ImageIcon("src/images/voetbal.PNG");
        frame.setIconImage(icon.getImage());

        vraag1 = new Vraag1();
        vraag1.setBounds(0,0,1191,677);
        frame.add(vraag1);

        paneel = new MainPanel();
        paneel.setBounds(0,0,1191,677);
        frame.add(paneel);     

        start = new StartScherm();
        start.setBounds(0,0,1191,677);
        frame.add(start);

        frame.setVisible(true); 

        }       
}