Prime.java

public class Prime {

    /**
    *   Program:    Prime.java
    *   Purpose:    Print out all prime numbers up to 1000
    *   Creator:    Chris Clarke
    *   Created:    12.04.2012
    *   Modified:   06.10.2012 Square root , comments added.
    */

    public static void main(String[] args) {

        for (int n = 1; n <= 1000; n++)
            if (isPrime(n))
                System.out.println(n);

    } // end main

    public static boolean isPrime(int k) {

        if (k<2)
            return false;           // 1 has only 1 unique divisor: itself
                            // ( so it's not prime)

        int sqrt = (int) Math.sqrt(k);      // calculate square root of k

        for (int j=2; j<=sqrt; j++)     // iterate from 2 to square root of k
            if (k%j==0)         // if j is a divisor of k...
                return false;       // ...k is not prime

        return true;                // if flow gets here, k must be prime

    } // end isPrime
} // end class