为什么我在这里得到一个空指针异常？

Question

I am using java. The second line of this code is getting a null pointer exception.

double gpa = 0.0;
gpa = grads[index].calculateGPA();
return gpa;

grads is an array of Graduate objects. I have tested this method in a JUnitTest and it works fine. I have also tested calculateGPA(). Only when I run the program there is an error.

Answer 1

The error could be caused by one of the following possibilities:

1. grads is null .
2. index is null .
3. grads[index] is null .
4. calculateGPA() is raising a null pointer exception.

Use your debugger to find out which of these possibilities it is, and take it from there.