I've been working on a project that allows a user to create an AI that gets wrapped and used in a project.
Java Code: 
firstPlayer = Class.forName(player1FileName);
player1 = (player) firstPlayer.newInstance();
Now say I want to make sure that player1FileName is not a dirty tricky little file. Any suggestions on how to keep an eye on what they can and cannot do?

First let me give you a little background. This doesn't have to be 100% secure, as just friends/faculty will be using this code for personal use. It will likely be trashed soon after the project is complete and played with.

My thoughts were you check and control which imports they use. Any ideas how I can check to see what they have imported?

They are handing me a .class file, I won't have access to the .java.

I appreciate any help. Thanks!