Casting

[rhett howard]

Hey guys,
I have a question about casting in this code from one of the devaka K examlabs........

Kinda confused with the whole typecasting thing.......


class B extends A{}
final class C extends B{}

class A{
public static void main(String args[])
{
A a = new B();
B b = new B();
C c = new C();
C[] ca = null;
a = b;
b = c;
A a1 = (B) c;
Runnable r1 = (Runnable) a; //1
Runnable [] ra1 = null;
A r2 = (A) r1;
A[] aa1 = (A[])r1; //17
A[] aa2 = (A[])ra1; //18
ra1 = (Runnable[]) ca; //19
}
}



Why is line 19 giving compile time error when line 18 isn't?

Thanks in advance!!!

[rhett howard]

Even //1 doesn't compille when i say


Runnable r1 = (runnable) c;


Is it because class c is final???...


If that is so, I am even more confused???

[rhett howard]

Okie, I understand it something like this......

Since C can't be subclassed anymore, compiler figures out there can't be any subclass which can implement Runnable and so it won't allow any casting to runnable???.......

Looks like thats the answer!!.....Let me know if it isn't......

Now i wonder why i even posted this question???......

[Bob Wheeler]

rhett howard wrote:
Okie, I understand it something like this......

Since C can't be subclassed anymore, compiler figures out there can't be any subclass which can implement Runnable and so it won't allow any casting to runnable???.......

Yeah, that's it.

rhett howard wrote:
Now i wonder why i even posted this question???......

Let see it is as a therapy. Loud thinking. You listen to your echo and understand the problem. It works most of the time.

cheers
Bob