code: protected static boolean isNumeric(String s)
      {
          for (char c : s.toCharArray())
          {
              if (!Character.isDigit(c))
                  return false;
          }
          return true;
      }
docs: Determines if a string contains only digits.
  
  @param s String to test.
  
  @return {@code true} if {@code s} contains only digits.