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Casting

 
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Hi,
Which statements, when inserted at the indicated position in the following code, will cause a runtime exception when attempting to run the program?
class A {}
class B extends A {}
class C extends A {}
public class Q3ae4 {
public static void main(String args[]) {
A x = new A();
B y = new B();
C z = new C();
// insert statement here
}
}
A. x=y;
B. z=x;
C. y = (B)x;
D. z = (C)y;
E. y = (A)y;
The answer given was C. x is handle for A and it was assigned to B handle by casting to B. Was it legal? Somebody please explain.
 
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Choice A Will compile and run fine. Choices B, D, E won't even compile. C will compile but will throw a ClassCastException.
The compiler allows the cast, since x is a superclass reference but at runtime can point to a subclass object.
HTH
------------------
Velmurugan Periasamy
Sun Certified Java Programmer
----------------------
Study notes for Sun Java Certification
http://www.geocities.com/velmurugan_p/
 
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