Java modifier types (public, protected, Private, friendly)

Java modifier types (public, protected, Private, friendly)

Public classes, class variables and methods, any class in and out of the package can be accessed;
Protected classes, class variables and methods, any classes in the package, and those outside the package that inherit this class can be accessed;
Private classes, class variables, and methods are not accessible to any class outside the package;
If a class, category variable, and method are not modified with these three modifiers, it is of the friendly type, then any class in the package can access it, any class outside the package cannot access it (including the subclass that inherits this class outside the package). Therefore, this type, class variables, and methods are friendly to other classes in the package, is open, while other classes outside the package are closed.