Prime numbers example in Java?

Prime numbers are 2,3,5,7,11,13,17,19....etc.

Here is the example to print prime numbers below 20.

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class primeNumbers {

public static void main(String[] args) {

int i=0;
int num=0;

for(i=1;i<20;i++){
int count=0;
for(num=i;num>=1;num--){

if(i%num==0){
count=count+1;
}

}

if(count==2){
System.out.println(i);

}
}
}
}