public class Test {
 
    public static void main (String[] args) {
        String first = "joe";
        String last = "blogg";
        String username = take(first, 1) + take(last, 6);
 
        System.out.println("first: [" + first + "] last: [" + last + "] " +
                           "username: [" + username + "]");
 
        last = "blog";
        username = take(first, 1) + take(last, 6);
 
        System.out.println("first: [" + first + "] last: [" + last + "] " +
                           "username: [" + username + "]");
    }
 
 
    /*
     * Returns a substring consisting of the first n characters of
     * a string, or else the whole string if it has less than n
     * characters.
     */
    static String take(String str, int n) {
        String substr;
 
        if (str.length() > n) {
            substr = str.substring(0, n);
        }
        else {
            substr = str;
        }
        return substr;
    }
}

// Take the minimum of 6 and the surname length.
int len = Math.min(6, surname.length());
 
userid = forename.substring(0,1) + surname.substring(0,len);