It appears you do not know at what time to use what method. For example, take lines 7 and 8. The first line starts with 'getWorld' which is an Actor class method and the second starts with 'addObject' which is World class method. Unless you wrote one (or both) of those methods into this class, there is a definite problem. The class cannot be both an Actor subclass AND a World subclass, so one of the two lines is faulty. All non-static methods are executed on an object. The object is given before the call. For example: When the object is not given before the call, the object is the same as the object the code is currently being executed for (or on). Since 'getWorld' is an Actor class method, you cannot start a line with it in a World subclass; only in an Actor subclass. The same goes with 'getOneObjectAtOffset'. If the 'GameOver' method is in a World subclass, you cannot start a line with that. You need to execute the method on an Actor object. Even then, because the method is protected, you cannot even use it outside an Actor subclass. Line 5 is bad in that a single equal sign will set Player to 'null' and 'null' is not a boolean and cannot be used as a condition in an 'if' statement. Sidenote: fields, like your 'Player' field, by convention, should begin with a lowercase letter. One last thing, if (1500, 1500) is the center of your world then your world would be 3000x3000. Everyone will end up with scrollbars and no one will want to play your 'small', as you described above, game. I personally would try not to exceed 800 to 1000 x 600.