k&b master exam :polymorphism doubt

[Nisha Pinjarkar]

This is a que from k&b book. The answer is "An exception is thrown at runtime.
Can someone explain it to me pls? Thanks.

class X{void go(){System.out.print("x";}}
class Y extends X{void go(){System.out.print("y";}}
class Z extends X{void go(){System.out.print("z";}}
class Chrome2{
public static void main(String [] args)}
X z = new Z();
X y = new Y();
Z y2 = (Z)y;
z.go();
y.go();
y2.go();

}

}

[anil kumar]

Hi

Nisha
-----------------------
Z y2 = (Z)y;
-----------------------
Exception will come here

the run time type of y is Y.
So there is no relation between class Y and class Z.


--------------------------------------------------------
class X{void go(){System.out.print("x";}}
class Y extends X{void go(){System.out.print("y";}}
class Z extends X{void go(){System.out.print("z";}}
-----------------------------------------------------

See the declarations carefully

Y IS-A X
Z IS-A X

There is no Z IS-A Y.


Thanks

Anil Kumar

[Gitesh Ramchandani]

Anil is right.

As there is no relationship existing between y and Z, you cannot cast Y to a Z.

regards,
Gitesh
[ May 22, 2007: Message edited by: Gitesh R ]

[Nisha Pinjarkar]

Thanks Anil !