Java default modifier

Public classes, generic variables and methods, and any class within and outside the package can be accessed;
Protected classes, generic variables and methods, any class within the package, and those outside the package that inherit from this class can be accessed;
Private class, generic variables and methods, any class outside the package can not be accessed;
If a class, generic variable, and method are not decorated with these three modifiers, then any class within the package can access it, and any class outside the package
Cannot access it (including subclasses that inherit this class outside of the package), so such, generic variables and methods are friendly and open to other classes within the package, while other classes outside the package are closed

Java default modifier