code: public static boolean isWhitespace(String s) {
          // Is s empty?
          if (isEmpty(s)) return true;
  
          // Search through string's characters one by one
          // until we find a non-whitespace character.
          // When we do, return false; if we don't, return true.
          for (int i = 0; i < s.length(); i++) {
              // Check that current character isn't whitespace.
              char c = s.charAt(i);
  
              if (whitespace.indexOf(c) == -1) return false;
          }
          // All characters are whitespace.
          return true;
      }
docs: Returns true if string s is empty or whitespace characters only.