Because -1 and 9 are integers, so -1/9 is an integer division (with the result 0, which when cast to double is 0.0).
To do a floating point division, you should convert one of the numbers to double, (double) 9, 9d or simply 9.0.
In the latter case, fraction is already double (-1.0) so fraction/9 is a floating point division.
