why is string value not changed?

Question

Hi

string is reference type, so why do i get this with the code below: Joe Joe Bill, Joe?

I would expect Joe Joe Bill, Bill because string is not a value variable.

Thanks again

            string str = "Joe";
            string str2 = str;
            Console.WriteLine(str);
            Console.WriteLine(str2);

            str = "Bill";
            Console.WriteLine(str);
            Console.WriteLine(str2);