I don't know why but it never worked for me either.
What i do to implement Overriden methods, or getters/setters or things
like that is pressing
ctrl+enter (in Mac, i don't know if it's
the same combination in other OS), which prompts a dialog showing some
options in which you can find Override:
Hope this helps you :)
(I'd have posted an image showing you but i don't have enough