NullPointerException when declaring semaphores in Java?

Question

I get aNullPointerException when I try to run this code:

private static Semaphore[] trackSemas;

for(int i=0;i<9;i++){
            trackSemas[i] = new Semaphore(1,true);
        }

Why doesn't this bit of code get a NullPointerException?

Answer 1

You need to initialize the trackSemas array:

private static Semaphore[] trackSemas = new Semaphore[9];