Difference between local variable initialize null and not initialize?

Question

In Java, what is the difference and best way to do?

Integer x = null; // x later assign some value.
Integer y; // y later initialize and use it.

Answer 1

No differences at all expect for one thing, if you don't initialize it and later on you try to use this variable (without changing the reference) means an error at compilation time, but if you initialize it and you use it later on (without changing the reference) means a NullPointerException.

I show you with an example.

Without initializing

Integer y;
y.intValue(); // Compilation error

With initializing

Integer x = null;
x.intValue(); // You are able to compile it but NullPointerException