You wouldn’t need floor/ceil for that. Casting a double to an int is already predictable as the java language spec explicitly says how to do it, so any JVM will do this the exact same way.
The floor/ceil functions are simply primitive math operations and they are meant to be used when doing floating point math.
All math functions return the same type as their input parameters, which makes sense. The only exception are those that are explicitly meant for converting between types.