What should this game over screen do? If you just want a game over screen you just need a new class with an image which you add to the world when your character dies. You could also remove all the objects in the world before doing this or stop the execution of the game. To stop the game you just need to call Greenfoot.stop(); To remove all the objects you can use this code: If you also need something else just ask.

As an alternative, after removing all the actors from the world, you can set a new background image to the world (the game over screen) and call 'Greenfoot.stop();'. This avoids adding another Actor class for something that really has no actions or influential purpose in the world (as far as interacting with other actors).

To remove all objects in the world you can use this: But I don't realy understand what you mean by if character is !null. Could you explain that?

Ive got this

You need to create a new class GameOver or any other name, set the image of this actor to the game over screen and add it to the world. So in line 9 you add this:

Or, since you removed all the actors, just change the background image of the world to your game over screen:

I tried setting up the world.setBackground("game_over.jpg"); Greenfoot.stop(); but cannot get it to work. I am a Greenfoot newbie, where do I place this in my code (in the class where my collision/stop occurs?) & do I need to create a game_over class under the World class? Thanks!

You had this: You should be able to get it to work if you place it at line 7 above.

I'm using the Greenfoot book Asteroids game as an example to try this, where do I place this in my code? checkCollision( )? private void checkCollision() { Asteroid a = (Asteroid) getOneIntersectingObject(Asteroid.class); if(a != null) { getWorld().addObject(new Explosion(), getX(), getY()); getWorld().removeObject(this); //here?? } }

I keep getting "java.lang.NullPointerException" and "java.lang.IllegalStateException: Actor not in world. An attempt was made to use the actor's location while it is not in the world. Either it has not yet been inserted, or it has been removed" errors, so I must be placing this incorrectly in the code.

Note line 5 in my last post. It sets up a local variable to hold the world the actor is currently in. In the code you just posted, you are not doing that and are not able to access the world after you remove the actor from it. Hence, your error messages.