Java: Prime Number Program Not Working -

why int j value 2? doesn't (int)realnum mean must natural number?

scanner basicnum = new scanner(system. in ); string insertnum = joptionpane.showinputdialog(null, "insert number\n");  int realnum = integer.parseint(insertnum); int j = realnum = 1;  if (realnum < 10000) {     while ((realnum / j == (int) realnum)) {         j++;     }     system.out.println(j);     if (j > 2) {         joptionpane.showmessagedialog(null, "it not prime!!");     }      if (j < 2) {         joptionpane.showmessagedialog(null, "it prime!");     } } else {     joptionpane.showmessagedialog(null, "too large number!"); } 

in java 8, can this:

boolean isprime(final int n) {     return intstream.range(2, n / 2+1).nonematch(i -> n % == 0); } 

on earlier versions, 1 should same work,

    string insertnum = joptionpane.showinputdialog(null, "insert number\n");     int realnum = integer.parseint(insertnum);     boolean prime = true;     (int = 2; <= realnum / 2; i++) {          if (realnum % == 0) {               joptionpane.showmessagedialog(null, "it not prime!!");               prime = false;               break;          }     }     if (prime) {          joptionpane.showmessagedialog(null, "it prime!");     }