In reply to shobhana.swarnkar18:
If you meant to say with a clear example:
class A;
int member1;
endclass
class A1 extends A;
int member2;
endclass
class A2 extends A;
int member3;
endclass
A1 a1_h = new();
A2 a2_h;
// this is not legal
a2_h = a1_h;
There no cast that would make it legal. a2_h.member3 does not exit in the constructed object.