Question 5Given:10. interface Foo {}11. class Alpha implements Foo { }12. class Beta extends Alpha {}13. class Delta extends Beta {14. public static void main( String[] args) {15. Beta x = new Beta();16. // insert code here17. }18. }Which code, inserted at line 16, will cause ajava.lang.ClassCastException?

technology programming languages

  1. B. Foo f= (Delta)x;

  2. A. Alpha a = x;

  3. D. The code on line 31 throws an exception.

  4. C. Foo f= (Alpha)x; D. Beta b = (Beta)(Alpha)x;

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Correct Option: A

AI Explanation

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) Foo f = (Delta)x; - This option is incorrect because it is casting the object 'x' of type Beta to type Delta. Since Beta is a subclass of Delta, this cast is valid and will not throw a ClassCastException.

Option B) Alpha a = x; - This option is incorrect because it is assigning the object 'x' of type Beta to a reference variable 'a' of type Alpha. Since Beta is a subclass of Alpha, this assignment is valid and will not throw a ClassCastException.

Option C) The code on line 31 throws an exception. - This option is incorrect because line 31 is not present in the given code.

Option D) Foo f = (Alpha)x; - This option is incorrect because it is casting the object 'x' of type Beta to type Alpha. Since Beta is a subclass of Alpha, this cast is valid and will not throw a ClassCastException.

Option E) Beta b = (Beta)(Alpha)x; - This option is incorrect because it is casting the object 'x' of type Beta to type Beta. Since Beta is already of type Beta, this cast is unnecessary and will not throw a ClassCastException.

The correct answer is A) Foo f = (Delta)x;. This option is incorrect because it is casting the object 'x' of type Beta to type Delta. Since Beta is not a subclass of Delta, this cast is invalid and will throw a ClassCastException.

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