public class Es1309 {

  public static void main(String args[]) {
    JButton b1 = new JButton("Contatore 1");
    JLabel l1 = new JLabel("valore 0");
    JLabel lab = new JLabel("Bottoni con pressioni uguali");
    ...
    JPanel panel = new JPanel();

    EsameFrame frame= new EsameFrame("La somma vale 0", ...);
    Container c = frame.getContentPane();
    c.add(panel);
    ...
    b1.addActionListener (frame);
    frame.show();
  }
}