How to find the prime number and not a prime number using java program

Program to find the prime number and not a prime number using java program

import java.util.*;

public class Main{

public static viod main(String arrg[]){

int num = 29;
boolean flag;
for (int i =2 ; i<=num/2; i++){

if (num % i ==0)
{
flag = true;
break;
}
}

if (!flag){
System.out.println("Prime number);
}

else{
System.out.println("Not a Prime number);
}
}
}