ID generator comparison

nimo23 :

I want to generate an unique ID within my application which can be used as a primary key for my database. The ID should be created by the application (and not by the database). I am wondering which method should I better use for that:

version 1:

// maybe faster and more memory friendly than version 2
// but what about collisions?
var uniqueId = ThreadLocalRandom.current().nextInt()

or version 2:

var uniqueId = UUID.randomUUID().toString()

or version 3:

// maybe the same as version 1
var uniqueId = new SecureRandom().nextInt()

or anything better?

ciamej :

Both versions 1 and 3 will produce collisions, because there are only 2^32 different int's. You need to calculate the probability yourself.

Regular UUIDs (version 2) are also random, but there is 2^128 of them, which means the chances of a collision are negligible.