I've been working on this code to check whether no is prime or not the problem is i cannot understand syntax plz help

I am using this code to find whether a no is prime or not the problem is in the for loop i cannot understand why we need to us this condn statment (i<=num/i). Please i don't have problem in syntax i have problem in understanding how the loop works just (i<=num/i) condn. ****/******* package javalearning; // This code tries to check the whether no is prime or not by divinding it with 2 3 4 and so on .. until the the divisor is less then or equal to the dividend/divisor import java.util.Scanner; public class forDemo {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner input=new Scanner(System.in);
    int num=input.nextInt();
    boolean isPrime=false;
    // this code is to illustrates prime no test using for loop
    for (int i=2; i<=num;i++)
    {
        if (num%i==0 ) {isPrime=false; break;}
        else isPrime=true;
    }
    System.out.println("IS YOUR NO A PRIME : "+isPrime);
}

} /************/************** Plese forgive me for using long line of codes. Thanks for help