public class blueBall extends Ball { public void act() { move(); turn(); } public void turn() { if (isAtEdge()) { turn(Greenfoot.getRandomNumber(90)); } } }

The only thing that determines which direction the ball is moving is its rotation. You will need to give it a random rotation when created and then adjust it in your 'turn' method depending on which edge the ball is at. Because you need to know which edge is touched, using the 'isAtEdge' method seems inappropriate as you would have to duplicate the checks it performs because it does not return any value to inform the calling method which edge, if any, is touched (it only tells you whether one is touched or not by returning a boolean, or true/false value). The documentation of the 'isAtEdge' method tells you what kind of checks it performs.

Oh okay that makes sense. Is there another method already in the documentation that would be better or will I have to create one to find which specific edge it is?

Just use the 'getX' and 'getY' methods and compare the returned values to that of the edges of the world: left edge: getX() == 0 right edge: getX() == getWorld().getWidth()-1 top edge: getY() == 0 bottom edge: getY() == getWorld().getHeight()-1 The change in rotation of the ball will be different for each edge, so code each bounce individually (use a separate 'if' block for each edge).

On further consideration, the change in rotation for opposite edges would be similar and, therefore, you can reduce the four 'if' block' to two of them ORing (using ' || ' ) the checks for opposite edges. For example, for the top and bottom edges (when getY() is in question), you can use: The change for the other two sides is a bit different. See if you can figure it out.

That seems to be working, it was really simple but took some time.

You might want to use the DriftMove class which I have created. It allows you to make an object drift on the screen and features a BounceAtEdge method that reflects at the angle that it hits the edge, just like a regular ball. It also allows you to set a random speed on spawning, and a number of other methods that might help. You can find it here: http://mrstewartslessons.com/useful_class_driftmove.html Select-click on the 'Download Class' and save it in your project folder. Close your project and open it again, and the class will be in there. Double-click on the class and change 'Source Code' to 'Documentation' to see very clear explanations of how to use the class. Hope it helps!