code: public static boolean isSSN(String s) {
          if (isEmpty(s)) return defaultEmptyOK;
  
          String normalizedSSN = stripCharsInBag(s, SSNDelimiters);
  
          return (isInteger(normalizedSSN) && normalizedSSN.length() == digitsInSocialSecurityNumber);
      }
docs: isSSN returns true if string s is a valid U.S. Social Security Number.  Must be 9 digits.