A simple modulus based algorithm used in Java to find if the passed number is prime or not.

1. private boolean IsPrime(int i)
2. {
3. if (i <= 1) return false;
4. if (i == 2) return true;
5. if (i % 2 == 0) return false;
6. int n = (int)Math.round(Math.sqrt(i));
8. for (int x = 3; x <= n; x += 2)
9. {
10.  // If it divides, it's not a prime
11.  if (i % x == 0)
12.  {
13. return false;
14.  }
15. }
16. // If we got to this point, the number is prime
17. return true;
18. }