Preventing Instances of the subclasses from accessing each others protected methods

Hello,

I have two subclasses A1 and A2 that have a common superclass S which is handle class. I have a protected method in the superclass S. Lets call it pm.

In subclass A1, I have a private variable that has a reference to an object of class A2.

I create two objects O1 and O2, where O1 is an instance of A1 and O2 is an instance of A2, respectively. O1 has access to O2 through its private variable I described earlier. I initially thought that O1 can only call the public methods of O2 and the not protected methods, i.e., pm in this case. But it seems that O1 can call the protected methods of O2.

Is there a way to prevent this? I was thinking that despite them sharing a common superclass, instances should only be allowed to acces public methods.

Answer 1

[Adarsh]

Hi @philly,

I understand that you want to prevent the access of protected member functions in a subclass “A2” to be restricted from other subclasses “A1” which inherit the same superclass “S”.

According to inheritance rules in Object Oriented programming, a protected member of the superclass can be accessed from the superclass and any of the subclasses, so you cannot directly restrict this access using Access modifiers.

However, there are few alternative ways in which you can restrict this access, they are:

1. If your code permits you can move the implementation of the function to be protected from superclass to subclasses.
2. You can setup a new class called the “Mediator” class as a wrapper class which contains the instance to the “A2” class with “private” access and allows only an interface will select methods to be called. Now an Instance of this class can be stored in “A1” to have controlled access for “A1” to “A2”.

The example implementation for the second method is as follows:

% Middle Person class for A2
classdef A2Mediator
    properties (Access = private)
        a2Instance
    end
    
    methods
        function obj = A2Mediator(a2)
            obj.a2Instance = a2;
        end
        
        function publicMethod(obj)
            obj.a2Instance.publicMethod();
        end
        
        function safePmAccess(obj)
            obj.a2Instance.safePmAccess();
        end
    end
end

This mediator interface only allows required functions to be visible for outside to access which can easily be controlled.

For more information regarding the “Subclassing” and “Inheritance” please refer to the following documentation link:

https://www.mathworks.com/help/simscape/lang/subclassing-and-inheritance.html

I hope this helps.