code: public static int addExact(int a, int b) {
          long result = (long) a + b;
          checkNoOverflow(result == (int) result);
          return (int) result;
      }
docs: Returns the sum of {@code a} and {@code b}, provided it does not overflow.
  
  @throws ArithmeticException if {@code a + b} overflows in signed {@code int} arithmetic