P p = new P();
C c = (C) p /// Gives ClassCastExeption.

1. A reference to any object can be cast into a reference to an object of class Object.

2. A reference to to an object can be cast into a reference to an object of class C', if the actual class of the object is a subclass of C'
3. A reference to an object can be cast into a reference to an object of interface I, if the actual class of the object implements I, or is of interface type I' and I' is a subinterface of I, or if the object is an array type and I is the Cloneable interface.
4.A reference to an object can be cast into a reference to an object an array type(with element reference type T), if the object is of an array type(with element reference type T') such that T' can be cast into T.

You need to go through these rules carefully and understand them well. I might also hint to you that downcast does not result into a compile error, for the compiler assumes that you really mean to do it that way, but it may result into a runtime error if your the rules above have not been observed. I have seen a few mock question where you need to chose between runtime Exception and compile time.

Best wishes for your exam

regards,

Whenever you see a cast with the explicit casting
ie., of type obj1 = (obj1)obj2
think about how it behaves at runtime. Usually casts like this cause ClassCastException at runtime rather than raise compile time errors.

On the other hand, if it is an implicit cast ie., of type
obj1 = obj2 using assignment or expressions involving object references, think like a Java compiler to see if it compiles fine.

This has worked for me fine in all of my mock tests. Let me know if you come across a problem where you cannot apply this rule. I will then try to refine it!!.

Thanks for the info - I understand this part. But some questions from Bill Brogden book bother me. I guess, I should ask those specifically. I do not have that book with me today. May be tomorrow, I will post those questions.