Why 2^31 is not divisible by n?

Question

http://docs.oracle.com/javase/6/docs/api/java/util/Random.html#nextInt%28int%29 says:

The algorithm is slightly tricky. It rejects values that would r

Answer 1

Regarding the first question:

As I understand the sentence, it's said that an uneven distribution is caused when 2^31 is not divisible by n.

I'm sorry but I don't know for the second question.