command line output

the below is command line output generated from the (further below) main method

Factorial of '31' is '738197504'
Factorial of '10' is '3628800'
Factorial of '5' is '120'
Factorial of '4' is '24'
Factorial of '3' is '6'
Factorial of '2' is '2'
Factorial of '1' is '1'
Factorial of '0' is '1'
Attempted factorial of '-1'. Factorials of negative integers are undefined.
Attempted factorial of '-2'. Factorials of negative integers are undefined.
Attempted factorial of '-8'. Factorials of negative integers are undefined.

gistfile1.java

/**
 * Calculates factorial values. One thing this class doesn't do is handle large factorials appropriately.
 * @author Zak Taccardi
 */
public class FactorialMaker {
    public static final int UNDEFINED_OPERATION = -1;
    /**
     * Calculates a factorial for a number
     * @param num the int to do a factorial with
     * @return the result of the factorial calculation. If the value is undefined, this method returns -1
     */
    public static int doFactorial(int num){
        int r = 1;
        if(num > 1) {
            int i = num;
            while (i > 1){ //no point running again when i == 1, because 'r' * 1 is always 'r'
                r *= i;
                i--;
            }
            printFactorial(num, r);
            return r;
        } else if (num == 0 || num == 1) {
            printFactorial(num, r);
            return 1; //0! and 1! are always 1
        } else if (num <= -1){
            System.out.println("Attempted factorial of '" + num +"'. Factorials of negative integers are undefined.");
            return UNDEFINED_OPERATION;
        } else
            return UNDEFINED_OPERATION;
    }
    
    //handles basic printing do command line
    private static void printFactorial(int initialValue, int result){
        System.out.println("Factorial of '" + initialValue + "' is '" + result + "'");
    }
    
    public static void main(String [] args){
        doFactorial(31);
        doFactorial(10);
        doFactorial(5);
        doFactorial(4);
        doFactorial(3);
        doFactorial(2);
        doFactorial(1);
        doFactorial(0);
        doFactorial(-1);
        doFactorial(-2);
        doFactorial(-8);
    }

}