Because Java is static and relatively simple, the level of autocompletion is absolutely fantastic. E.g. a simple case, typing:
int a = obj.
Would show first only methods that return integers. But this gets far more sophisticated with completion anticipating your preference, naming variables for you, filling in the parameters with sensible values etc.
Going back to the simple list of options is a bit of a pain. Also, this needs to be written in Java since it needs to read the API classes to make suggestions. But his editor code is probably in Swift.
Genuine question.