Primes

Recursively:

package mainPackage;
public class Playground {

	public static void main(String[] args) { // Always need this
		isDivisible(13, 2)
	}
    
	private static boolean isPrime(int x) {
		if (x <= 1) 
			return false;
		else
			return ! isDivisible(x, 2);
	}
	
	private static boolean isDivisible(int x, int k) {
		if (k >= x)
			return false;
		else if (x % k == 0)
			return true;
		else
			return isDivisible(x, k+1);
	}
}

Print all primes up to and including LIMIT, 10 to a line.

private static void printPrimes(int limit) {
    int np;
    np = 0;
    for (int p = 2; p <= limit; p += 1) {
        if (isPrime(p)) {
            System.out.print(p + " ");
            np += 1;
            if (np % 10 == 0)
                System.out.println();
        }
    }
    if (np % 10 != 0)
        System.out.println();
}