Casting & Converting using Object Refrence

[suresh kamsa]

Can any one explain me about object refrence converting and casting using examples classes,interfaces etc.
Thanks.

[Thomas Paul]

Why not try to narrow your focus a little. Why not tell us what is confusing you.

[suresh kamsa]

I read about Casting and converting in RHE book. I understood what they were talking about. But when I was trying to solve some questions from DAN's mock exam I am not able to do anything. I am getting confused at using interfaces when we are doing object refrence.
I understood object refrence in upward hierarchy is possible not in downwards.
Ex
class a
class b extends a
b b1 = new b;
a = b1;
It is possible because b is a subclass of a.
When it comes to Interfaces I have know idea.
Thanks for asking me about my confustion part.

[zarina mohammad]

When it comes to interface a class can be cast to interface implicitly if the class implements the interface.
But explicit conversion is needed to cast an interface to class implementing the interface(which is legal even at runtime) or to a class not implementing the interface(illegal at runtime)
this example might help you understand better

 interface baseinterface{}
class base implements baseinterface{}
class sub extends base{}
public class expCast {
  public static void main(String args[]) {
        base b=new base();
        sub s=new sub();
        baseinterface bi=new base();
        s=(sub)b;//illegal at runtime
        s=(sub)bi;//illegal at runtime
        b=(base)bi;//legal even at runtime
        }
    }