Object Casting

[GK]

Which of the following answers are correct n y???
----------------------
class AA extends Object implements I1
{
}
class BB extends AA implements I2
{
}
interface I1
{
}
interface I2
{
}
--------
Given
AA a = new AA();
BB b = new BB();
------------
OPTIONS
1)Object o = a;
I1 i1 = o;
2)Object o = a;
I1 i1 = (I1)o;
3)Object o = a;
I2 i2 = (I2)a;
4)Object o = b;
I2 i2 = o;
---------
GUNJAN

[huiying li]

The answer is 2.
1) 4)are wrong because explict casting is required in down casting
3) is wrong because a is a object of class AA, which does not implement I2

[GK]

Originally posted by gunjan kuwadia:
Which of the following answers are correct n y???

Can u explain me???
GUNJAN

[Hima Mangal]

for detailed explanation, you can refer to Chapter 4 of the Heller book
------------------
Hima

[puneet pruthi]

Hi gunjan
remember two main facts abt casting
1.At compile time,it will check if the two objects can denote an object of a class,where this class is subtype of both source and destination.
Otherwise it will give compile time error.
2.if it compiles then at run time it will check for the cast.
suppose the cast is
(abc)dest
if dest instanceof abc returns true,then it is a valid cast otherwise it will give class cast exception.