private char validateCharacter(char c) {
            if (c >= 'A' && c <= 'Z') {
                c = (char) (c - 'A' + 'a');
            } else if ((c < 'a' || c > 'z') && (c < '0' || c > '9')) {
                c = ' ';
            }
            
            return c;
        }