I wrote a tetris clone using Processing.org. I used no game framework and simply graphic and tweening libraries. I did it in about 6 weeks during a vacation between contracts. It was the hardest thing I had ever done at the time. I wrote a lengthy post about how I constructed it.
The source code is available here but it is not reference code by any stretch.
Downloads Tatris 0.5.0 for Mac
This game study has no associate with the Tetris LLC or it's properties. If the name constitutes a breach of copyright, please contact @squarism on twitter.