Multiple choice technology web technology

Given: 3. class A { } 4. class B extends A { } 5. public class ComingThru { 6. static String s = "-"; 7. public static void main(String[] args) { 8. A[] aa = new A[2]; 9. B[] ba = new B[2]; 10. sifter(aa); 11. sifter(ba); 12. sifter(7); 13. System.out.println(s); 14. } 15. static void sifter(A[]... a2) { s += "1"; } 16. static void sifter(B[]... b1) { s += "2"; } 17. static void sifter(B[] b1) { s += "3"; } 18. static void sifter(Object o) { s += "4"; } 19. } What is the result?

  1. -124

  2. -134

  3. -424

  4. -434

  5. -444

  6. Compilation fails
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The code tests Java's method overload resolution with varargs. sifter(aa) calls sifter(A[]... a2) matching -4. sifter(ba) matches sifter(B[] b1) NOT sifter(B[]... b1) because Java prefers non-varargs over varargs when both match - giving -3. sifter(7) matches sifter(Object o) as 7 autoboxes to Integer then widens to Object - giving -4. Final result: -434.

AI explanation

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

Option A) -124 - This option is incorrect because the result will not include the number 1.

Option B) -134 - This option is incorrect because the result will not include the number 1.

Option C) -424 - This option is incorrect because the result will not include the number 2.

Option D) -434 - This option is correct because the result will include the numbers 4 and 3.

Option E) -444 - This option is incorrect because the result will not include the number 2.

Option F) Compilation fails - This option is incorrect because the code compiles successfully.

The correct answer is D. This option is correct because the result will include the numbers 4 and 3.

Explanation:

  • The main method calls the method sifter with different types of arguments: an array of type A[], an array of type B[], and an integer (7).
  • There are multiple overloaded versions of the sifter method: one that takes an array of type A[], one that takes an array of type B[], one that takes an array of type B[] with a variable number of parameters, and one that takes an Object.
  • When sifter(aa) is called, it matches the sifter method that takes an array of type A[], so s += "1" is executed.
  • When sifter(ba) is called, it matches the sifter method that takes an array of type B[], so s += "2" is executed.
  • When sifter(7) is called, it does not match any of the sifter methods directly, but it matches the sifter method that takes an Object, so s += "4" is executed.
  • Therefore, the value of s becomes "-434".
  • Finally, the value of s is printed, which is "-434".

Thus, the correct answer is D.

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