What I meant to do was teach myself Java. What I ended up doing was writing an AI opponent for the above game in C++. Whoops.
Feel free to download the windows executable. It's not a finished product but I'm basically done working on it. It's not what many of you might recognize as a computer program because it lacks a graphical user interface and has no graphics, but I'm proud of the underlying logic. The level of difficulty is intended to be sufficiently challenging without being impossible. (Don't allow it any unchecked two-in-a-rows.)
If you yourself would like to make it GUI or add graphics or high scores or make any other improvements, feel free - here's the source. If you do download this, you must email me and let me know; if you improve it, make sure to acknowledge my role. Also, if you do enjoy the game but get frustrated at some of its limitations, let me know what bothers you and I may eventually improve it myself. Now that I have finally learned Java and have discovered the relative ease of GUI and graphics, what I'd like to eventually do is rewrite it into a pretty Java applet so that it could be played in a browser.