如何从java中的另一个类调用String或任何数据类型

I have a LoginGUI and a MainGUI, what I want to do is return the current user as a String or the UserID as an Integer in my MainGUI. My program runs the LoginGUI and then if the UserName a password match up with the database it lets you through to the MainGUI. I've declared a CurrUserID and CurrUser in my LoginGUI - both are public, but how can I use them in my MainGUI? I have a LoginGUI and a MainGUI, what I want to