// polymorphism/RTTI.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Downcasting & Runtime type information (RTTI)
// {ThrowsException}

class Useful {
 public void f() {}
 public void g() {}
}

class MoreUseful extends Useful {
 @Override
 public void f() {}
 @Override
 public void g() {}
 public void u() {}
 public void v() {}
 public void w() {}
}

public class RTTI {
 public static void main(String[] args) {
 Useful[] x = {
 new Useful(),
 new MoreUseful()
 };
 x[0].f();
 x[1].g();
 // Compile time: method not found in Useful:
 //- x[1].u();
 ((MoreUseful)x[1]).u(); // Downcast/RTTI
 ((MoreUseful)x[0]).u(); // Exception thrown
 }
}
/* Output:
___[ Error Output ]___
Exception in thread "main"
java.lang.ClassCastException: Useful cannot be cast to
MoreUseful
 at RTTI.main(RTTI.java:31)
*/