Optimized Trial Division Prime Number Checking

Wikipedia definition of a prime number: "A prime number (or a prime) is a natural number greater than 1 that has no positive divisorsother than 1 and itself."  On that page, if you scroll down a bit, you'll see "Testing Primality...".  The following is a little 'Trial Division' method of determining if an entered int is a prime.  It is obviously limited to small numbers (java int), and it is not as efficient as the 'deterministic' algorithms mentioned on that page (which are O(logⁱ(n) [iterative logarithmic], better than the presented code's ~ O(n^1/2)).  It does, however, skip over all even and numbers divisible by 3 (other than 2 and 3, which are valid input).

import java.util.Scanner; /**  * Checks if a given number is prime  * @author sshakil  *  */ public class PrimeNumberChecker {   public static void main(String[] args) {          Scanner input = new Scanner( System.in );      int a;     do {       a = input.nextInt();       System.out.println(isPrime(a));     } while(a!=0);   }      private static boolean isPrime(int a){     if (a!= 2 && a!=3 && (a%2==0  || a%3==0))       return false;     int sqrRoot = (int) Math.ceil(Math.sqrt(a));     int i = 2;     for (; i <= sqrRoot && i%2 !=0 ; i++) {       if(a%i == 0)         return false;     }     return true;   } }