This topic may be regarded as low leveled.

However so many buddies are stuglling with this issue that I'll no more keep silent.

 

Actually, it is not much complex as someone imagine, I will conclud with little words as follows:

 

Private = Grant Any code in this class . Reverse : code outside, including subclasses is denied.
Protected = Grant Any code in this class and subclasses of it. Code outside is denied.
Public = Grant Any code inside or outside.
Internal = Grant Any code inside this Assembly.