You must have forgotten which forum you were on. I am sure Henry won’t mind if I move this discussion. You also appear to have forgotten the code button. I shall go back to your code and use the code button, and you will see how much better it looks.
Class variables is another name for static fields. When you are in a static method, you are working at the level of the class, not at the level of an instance, so you cannot access any instance members of the class. Nor can you use the keywords this and super.
The reason is that when you are in a static method, there might be no instances of the class. So there are no instance fields you can access. Or there might be several instances; you cannot tell which instance to use. So static == no access to instance members.