Enthuware

abstract class Calculator
{
abstract void calculate();
public static void main(String[] args)
{
System.out.println("calculating");
Calculator x = null;
x.calculate();
}
}


HOW IS ABSTRACT CLASS INSTANTIATED ???

You can't instantiate an abstract class but you can instantiate an anonymous class that extends the abstract class as follows:
Same logic applies for an interface. So when you say you are instantiating an abstract class or an interface, it means you are actually instantiating an anonymous class that extends or implements the abstract class or interface.

BTW, in this question, nowhere is the Calculator class being instantiated.

I believe that the problem is that the Method is never overridden in a subclass and that the program will throw an exception to that effect.