Abstract class VS Concrete class
1. If we don’t know anything
about implementation just we have requirement specification
(100% Abstraction) then we should go for interface.
2. If we are talking about implementation
but not completely ( partial implementation) then we
should go for Abstract class.
GenericServlet & HTTPServlet.
3. If we are talking about implementation
completely and ready to provide service then we should
go for concrete class.