interface Alpha {
    void f();
}
class Beta implements Alpha {
    public void f() {
        System.out.println("Beta.f()");
    }
    public void g() {
        System.out.println("Beta.g()");
    }
}
public class Main {
    public static void main(String[] args) {
        Alpha a = new Beta();
        a.f();
        System.out.println(a.getClass().getName());
        try {
            Beta b = (Beta)a;
            b.g();
        } catch (Exception e) {
            System.out.println("Error");
        }
    }
}