OnJava8-Examples/polymorphism/RTTI.java

//: polymorphism/RTTI.java
// <20>2015 MindView LLC: see Copyright.txt
// 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
  }
} ///:~