Question

I’m looking at LinkedList class implementation in C# and I cannot understand how
Add method is hidden.

LinkedList implements ICollection which has an Add method. In the LinkedList class code the Add method is declared as:

void ICollection<T>.Add(T value);

How it is possible to have internal method which is declared in the interface?

Answer 1

The interface is implemented explicitly.

Explicilty implemented interface members can only be accessed through an instance of the implemented interface, like so:

LinkedList list;
((ICollection)list).Add(...)

Check this SO question and answer for more information: implicit vs explicit interface implementation