Bonus Master Exam

[Jemima Job]

This question in the bonus Master Exam for K&B book, I don't think the answer selected as correct is true, because I compiled successfully but during runtime it threw nullpointerexception.
1. long a1[][];
2. long []a2[];
3. a2 = new long[3][];
4. a1 = a2;
5. System.out.println(a1[1][0]);

Selected answer is

Compilation fails at line 4.

[Marlene Miller]

Hi Jemima. The second exam has this one error. Here are some comments by other people. Here