This means that the arr variable in your initArray method will refer to the same array that you pass to it in your main method, but it is a different variable from the arr variable in your main method.
You essentially pass the value null to it, then you assign a new array to arr in initArray, which is a different variable from arr in your main method, so nothing happens to your main method variable.
Instead, you could do something like this:
The mind is a strange and wonderful thing. I'm not sure that it will ever be able to figure itself out, everything else, maybe. From the atom to the universe, everything, except itself.