Save Game data

You can't save the world and resume it the next time you play. But you can save numbers and strings. For example the level which was reached. When starting the game, you need to get this data and build up the game with it. Use the UserInfo class.

Sure, in that case you don't need to do anything special to save the world. Just keep a reference to it handy (in a variable of type World) then use Greenfoot.setWorld(...) to restore it when you're ready.

That would get a reference to the current world within a method of an Actor object. After (or when) the new world is created, that reference must be passed and saved in that new world so that you can return to the world later. This would need to be done before the method is exited from as the reference is local to the method in which it is acquired.

Please supply the names of your worlds, specify which one is the main one and which one needs to keep a reference to the other. A brief description of what the worlds are for might also help (like: a game world, Welt class, temporarily going to a menu world, Menu class)