code: public static boolean isSignedInteger(String s) {
          if (isEmpty(s)) return defaultEmptyOK;
  
          try {
              Integer.parseInt(s);
  
              return true;
          } catch (Exception e) {
              return false;
          }
  
          // int startPos = 0;
          // boolean secondArg = defaultEmptyOK;
  
          // if(isSignedInteger.arguments.length > 1) secondArg = isSignedInteger.arguments[1];
  
          // skip leading + or -
          // if((s.charAt(0) == "-") ||(s.charAt(0) == "+") ) startPos = 1;
          // return(isInteger(s.substring(startPos, s.length), secondArg))
      }
docs: Returns true if all characters are numbers;
  first character is allowed to be + or - as well.
  
  Does not accept floating point, exponential notation, etc.