Srikanth, But we can do good logical thinking here to arrive at the answer, I suppose.
See ... Attributes could be part of ServletRequest interface itself irrespective of whether it is an HTTP flavour or not. This is because when you talk about a "scoping object" like request, we need to store attributes against it whether it is HttpServletRequest or ServletRequest. Got me?
Whereas consider setHeader(...), headers are inherent part of HTTP thus is unique method which is there in HttpServletRequest only.
Sessions are also inherent part of HTTP and so we dont have anything like Session and HttpSession interfaces.
Hope you got what I am saying ...
Nevertheless, memorising APIs is good
Regards,
Mani