class Useful {
public void f() {
}
public void g() {
}
}
class MoreUseful extends Useful {
public void f() {
}
public void g() {
}
public void u() {
}
public void v() {
}
public void w() {
}
}
public class MainClass {
public static void main(String[] args) {
Useful[] x = { new Useful(), new MoreUseful() };
x[0].f();
x[1].g();
// x[1].u();
((MoreUseful) x[1]).u(); // Downcast/RTTI
((MoreUseful) x[0]).u(); // Exception thrown
}
}