Countdown

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.awt.Window.Type;

import javax.swing.JPanel;
import javax.swing.JWindow;


public class Frame extends JPanel {

    int atual = 5;

    public Frame(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                while(atual > 0){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {}
                    atual--;


                    removeAll();
                    revalidate();
                    repaint();
                }
                System.exit(0);
            }
        }).start();
    }

    public static void main(String[] args) {

        JWindow frame = new JWindow();
        frame.setType(Type.POPUP);
        frame.setSize(200, 200);
        frame.setBackground(new Color(0, 0, 0, 0));
        frame.setAlwaysOnTop(true);

        Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
        frame.setLocation(d.width/2-frame.getSize().width/2, d.height/2-frame.getSize().height/2);


        Frame panel = new Frame();
        panel.setOpaque(false);
        frame.add(panel);


        frame.setVisible(true);



    }

    @Override
    public void paint(Graphics g) {
        g.setFont(new Font("Arial Black", Font.PLAIN, 100));
        g.drawString(Integer.toString(atual), 50, 100);
    }

}