Well, if you are just checking characters, I guess you can just check if the characters are letters or numbers. Or you can just check if it is in the printable ascii range, which should be from a value of 32 to 127.
You've been around JavaRanch long enough to know that we have a policy on screen names. Basically, it must consist of a first name, a space, and a last name, and not be obviously fictitious. Since yours does not conform with it, please take a moment to change it, which you can do right here.