Question

1. Please fill in the cells according to the given statements for each row. If the statement runs correctly, it returns true or false, in this case please state the output in the fourth column. If the statement gives an error (i.e. compile or runtime error), please indicate that by typing the corresponding column (2nd or 3rd column). For each item, please write a one-sentence explanation. Note that each row will contain only one result. (15 points in total) } class B {...} class C extends B { class X extends C { class Y extends C { X X = new X(); ... } Compile Time Error Runtime Error Output (true/false) Statements return (x instanceof B): Bb=x; return (b instanceof C): Bb=x; Yy=(Y) b; return (y instanceof B); return (x instanceof Y); Y y=x; return (y instanceof B);

Answer 1

All the subclasses inherited from a superclass are its instance. Also, as subclasses are instance of super class, subclass variable can be assigned to a variable of superclass.

Statements	Compiler Time Error	Runtime Error	Output (true/false)
return (x instance of B);			true (x is of X class which inherits from C which inherits from B)
B b = x; return (b instanceof C);			true (x is assigned to B but it retaines value of X => it inherits from C)
B b = x; Y y = (Y) b; return (y instanceof B);		x can be converted to X again but X and Y have no relation. But as the variable b could have been of class Y, this error is not caught at compile time.
return (x instanceof Y);	.X and Y have not relation and as this could be caught at compiler time itself. At compile-time that it will never be true. Therefore, it is assumed that this is not what the programmer meant
Y y = x; return (y instanceof B);	X cannot be typcasted to Y as they do not share any relation.