The getObjects method returns objects which are in the world when it is called. An object of a class which isn't an actor can't be added to the world. To get an object of a non-actor class, you can't use this method. You can use static methods from this class or you have to save a reference to the object.

If it's like this then Greenfoot should fix the doc which says: public <A> java.util.List<A> getObjects(java.lang.Class<A> cls) Get all the objects in the world, or all the objects of a particular class. If a class is specified as a parameter, only objects of that class (or its subclasses) will be returned.

Well, you could add another 'in the world' at the end of the first sentence if it isn't clear to you. It really wouldn't make much sense if the world keeps a reference to all objects which are created (but not added to world) and doesn't ever remove the reference.