If you finish early, consider adding extra features to your program to make it more interesting:

• Adding buttons or keypresses that auto-create patterns on the screen so you don't have to draw them by hand.
• Allowing the user to load the world from a file.
• Creating a sparse representation of the world (using a Map) so you don't waste memory on empty spaces.
• Auto-resizing the world (instead of having it wrap).
• Allowing the user to scroll, pan, or zoom a large world in the window.
• Analyzing the world to see if its stagnant, and automatically injecting new cells to make the pattern change.