Java Puzzlers spring to mind. There's a book [0], and some fun talks available on youtube [1][2][3].

[0]: http://www.javapuzzlers.com/

[1]: https://www.youtube.com/watch?v=wbp-3BJWsU8

[2]: https://www.youtube.com/watch?v=yGFok5AJAyc

[3]: https://www.youtube.com/watch?v=Wnzyp1aitb8