Why does Math.ceil return a double?

The range of double is greater than that of long. For example:

double x = Long.MAX_VALUE;
x = x * 1000;
x = Math.ceil(x);

What would you expect the last line to do if Math.ceil returned long?

Note that at very large values (positive or negative) the numbers end up being distributed very sparsely – so the next integer greater than integer x won’t be x + 1 if you see what I mean.