Check if interger is a prime...

primeNumber.java

 /*
     * An optimized to check if a number is prime or not.
     */
    public static boolean isPrime(int num) {
        if (num == 2 || num == 3) {
            return true;
        }

        if (num % 2 == 0 || num % 3 == 0) {
            return false;
        }

        for (int i = 3; i < Math.sqrt(num); i += 2) {
            if (num % i == 0 || num % Math.sqrt(num) == 0) {
                return false;
            }
        }
        return true;

    }


// Read more: http://java67.blogspot.com/2016/01/java-program-to-print-prime-numbers.html#ixzz3wzp2ng3g