casting

[sri123]

hi everybody,
class Parent {}
class DerivedOne extends Parent {}
class DerivedTwo extends Parent {}

Parent p = new Parent();
DerivedOne d1 = new DerivedOne();
DerivedTwo d2 = new DerivedTwo();
d2 = d1;

A. Illegal both at compile and runtime.
B. Legal at compile time, but may fail at runtime.
C. Legal at both compile and runtime
given answer is b.but i think ans is a.
2)class Parent {}
class DerivedOne extends Parent {}
class DerivedTwo extends Parent {}


Which of the following statements is correct for the following expression?
Parent p = new Parent();
DerivedOne d1 = new DerivedOne();
DerivedTwo d2 = new DerivedTwo();
d1 = (DerivedOne)d2;



A. Illegal both at compile and runtime.
B. Legal at compile time, but may fail at runtime.
C. Legal at both compile and runtime
given answer is a.i think it is b.
i am very confusing these two questions please explain me.
thanks.

[Doit]

Both won't compile.

[Mirko Froehlich]

In both cases, the correct answer is A. Assigning one sibling to another is never legal, neither using conversion or explicit casting. You can only automatically convert up the inheritance hierarchy, and you can only cast down the hierarchy (which possibly results in a ClassCastException at runtime).
-Mirko

Originally posted by sri123:

hi everybody,
class Parent {}
class DerivedOne extends Parent {}
class DerivedTwo extends Parent {}

Parent p = new Parent();
DerivedOne d1 = new DerivedOne();
DerivedTwo d2 = new DerivedTwo();
d2 = d1;

A. Illegal both at compile and runtime.
B. Legal at compile time, but may fail at runtime.
C. Legal at both compile and runtime
given answer is b.but i think ans is a.
2)class Parent {}
class DerivedOne extends Parent {}
class DerivedTwo extends Parent {}


Which of the following statements is correct for the following expression?
Parent p = new Parent();
DerivedOne d1 = new DerivedOne();
DerivedTwo d2 = new DerivedTwo();
d1 = (DerivedOne)d2;



A. Illegal both at compile and runtime.
B. Legal at compile time, but may fail at runtime.
C. Legal at both compile and runtime
given answer is a.i think it is b.
i am very confusing these two questions please explain me.
thanks.

[Anonymous]

neither will ever compile correctly.