@Duta, I cannot be sure. It was too long ago. This was like my 3rd project in Greenfoot. I am not sure if I was using static variables at that point. However, I noticed I had said that it compiled different each time; which indicates that it was probably something else.

There is another, older, scenario (2010/12/8) called 'Blocks' that has the same concept. It is at: http://www.greenfoot.org/scenarios/2253

A lot of folks have been asking about how to detect collisions, or how not to pass through objects, so I created this example which also has an example of how one can sub-class my 'Bar' class to give it some functionality.

And if you did upload it mistakenly, log on, go to your page (click on your name), select the scenario, and click on 'delete scenario'.