Convert a String with text to long? (Java) [duplicate]

This question already has an answer here:

• How to convert String to long in Java? 5 answers

I am really just starting out at programming and am currently learning from thenewboston: http://ift.tt/1P0Wi2z

I am looking into how I could (if I can at all) turn a String with text into a long data type. I want to make it so that anything below 0! is "undefined" and display it.

public class bucky {
    public static void main(String[] args){
        System.out.println(fact(-1));
    }

    public static long fact(long n){
        String s = "undefined";
        Long lObj1 = Long.valueOf(s);

        if(n <= 1 && n>=0)
            return 1;
        else if(n<0)
            return lObj1;
        else
            return n * fact(n-1);
    }
}

If you know a way in which I can convert this, please let me know. Thanks so much! Just starting out.