I would guess that you created (a bunch of) static GreenfootImages, it definitely looks like it's possible to create those images with the drawLine and fillRect the most complicated image looks the empty squares. (If you didn't use static images, then you probably could.)

@Nosson1459, actually there are no static images, although I could have made two of them static. The base images of both a non-selected (which a flag can be drawn on) and a selected cell (which a number can be drawn on) could have easily have been made static. And yes, everything was done with the use of graphics drawing commands.

nice. I pretty much gave up on mine when I realized that what I've been trying to do most likely can't be done the way I'm trying to do it. Can you publish the source so I can see how you made the 0 squares disappear?

@JeremyP02, apparently there is a problem with playing sound files (wav) at this time. Removed sound to prevent freezing browser. Thx.