/** 
 * A very small program for computing the factorial
 * of a number
 * 
 * @author gtowell
 * Created: Oct 18, 2021
 */
public class Factorial {
    public static void main(String[] args) {
        String[] defaultArgs = { "5" };
        if (args.length == 0) 
            args = defaultArgs;
        try {
            int fb = Integer.parseInt(args[0]);
            Factorial f = new Factorial();
            int b = f.factorial(fb);
            System.out.println(b);
        } catch (NumberFormatException nfe) {
            System.err.println("<<" + args[0] + ">> must be an integer");
        }
        
    }

    /**
     * Compute factorial recursively
     * @param n the number whose factorial you want to compute
     * @return the factorial of the given number
     */
    public int factorial(int n) {
        if (n == 1)
            return 1;
        if (n < 1)
            return 0;
        int f = factorial(n - 1);
        return f*n;
    }
}