Objects and there references

[Higgledy Smith]

class Super
{ int index = 5;
public void printVal()
{ System.out.println( "Super" );
}
}
class Sub extends Super
{ int index = 2;
public void printVal()
{ System.out.println( "Sub" );
}
}
public class Runner
{ public static void main( String argv[] )
{ Super sup = new Sub();
System.out.print( sup.index + "," );
sup.printVal();
}
}

Output: 5, Sub

Why does sup.index ref to value i in Super class? I thought being that my instance reference refers to an instance object of Sub() that it would display the value held in Sub i=2.

Can some one explain?

[Keith Lynn]

A reference to the instance variable of the object is bound at compile time and is based on the type of the reference. Method calls are bound at runtime and are based on the type of the object. So the reference variable is to the one in the Super class, and the method, since it is overridden in the subclass, is bound to the method in Sub.