UUID to unique integer id?

Question

I was wondering what the easiest way to convert a UUID to a unique integer would be? I have tried using the hash code but people tell me that it is not going to always be unique if i use the hash code?

So what is the easiest way? Is the hash code unique?

Answer 1

You are going to have a problem since the UUID is 128 bits and the int is only 32bit. You'll either have to accept the risk of collisions and try to fudge it to a smaller space (hashCode is probably a good way to do that) or find an alternative (use the UUID directly, map to a BigInteger - difficult to tell without knowing why)

Answer 2

Answering the How can I have a unique application wide Integer:

If it needs to be unique even after restarts or if you application is clustered you may use a Database sequence.

If it just needs to be unique during the runtime use a static AtomicInteger.

EDIT (example added):

public class Sequence {    private static final AtomicInteger counter = new AtomicInteger();    public static int nextValue() {     return counter.getAndIncrement();   } } 

Usage:

int nextValue = Sequence.nextValue(); 

This is thread safe (different threads will always receive distinct values, and no values will be "lost")