code: public static String rand(int size) {
          StringBuilder num = new StringBuilder();
          for (int i = 0; i < size; i++) {
              double a = Math.random() * 9;
              a = Math.ceil(a);
              int randomNum = new Double(a).intValue();
              num.append(randomNum);
          }
          return num.toString();
      }
docs: Generate a number of numeric strings randomly
  
  @param size string count
  @return return random string value