checking if a given integer is a prime number java

1public class Prime {
2
3    public static void main(String[] args) {
4
5        int num = 29;
6        boolean flag = false;
7        for(int i = 2; i <= num/2; ++i)
8        {
9            // condition for nonprime number
10            if(num % i == 0)
11            {
12                flag = true;
13                break;
14            }
15        }
16
17        if (!flag)
18            System.out.println(num + " is a prime number.");
19        else
20            System.out.println(num + " is not a prime number.");
21    }
22}