import javax.swing.JFrame;
import javax.swing.JButton;
class MeinButtonListener{
public void actionPerformed(){

}
}
public class Fenster
{
    public static void start(){
    JFrame fenster = new JFrame("Mein erstes echtes programm");
    fenster.setSize(800, 600);

    JButton button = new JButton("Computer Virus");
  button.addActionListener(new MeinButtonListener());
    fenster.add(button);

    fenster.setVisible(true);
    }
}