Today someone has posted a question, and after less than 30 minutes he also posted an answer to his own question. I've flagged the mods and they declined my flag.
If I remember well, in the past, user Makoto Kato did similar things, using M.SE as its own database, and he was highly criticized (suspended?) for doing so.
Is this now an accepted way to use M.SE?
Edit. For those who think this happened only once to this user, let me give at least another one: An isometry of Hilbert spaces using the Radon-Nikodym derivative. (Here he posted an answer after 12 minutes!)
Let me make my point a little clearer:
Is it okay to post a question you already know the answer with the only purpose to answer it by yourself?
Later Edit. There is a related question Can I post a question and an answer just because I think it helps others? and an interesting answer posted there by @quid.