The 32 is thee code fault indicated and the controller is shown below. Pretty much standard, I think. public static void main(String[] args) { SimEnviro2WithUI sim = new SimEnviro2WithUI(); Console c = new Console(sim); 32 c.setVisible(true); } public void init(Controller c) { super.init(c); display = new Display2D(450.0D, 400.0D, this); displayFrame = display.createFrame(); c.registerFrame(displayFrame); displayFrame.setVisible(true); portrayal = new ObjectGridPortrayal2D() { public Portrayal getDefaultPortrayal() { return new OvalPortrayal2D(Color.red, 1.0D) { public void draw(Object object, Graphics2D graphics, DrawInfo2D info) { if(object != null) { super.draw(object, graphics, info); } } }; } }; display.attach(this.portrayal, "von Neumann single offspring portrayal"); display.setBackdrop(Color.white); }