How can the servlet engine create objects of interfaces?help

Question

hello,
I have this basic fundamental query...when using servlets i noticed that so many methods in the HttpServlet class take as arguments objects of the type "Interface"..where as basic principle in java is u cant instantiate interfaces...interfaces r mere templates which u implement by ur own custom classes.
For example the doGet method recieves from the servlet engine(servlet container) two arguments which r HttpServletResponse object and HttpServletRequest object..and u use these further to make use of the methods of the inmterfaces..which again is a mystery to me...why?
here is why:-
since HttpServletResponse and HttpServletRequest r interfaces..they cant be instantiated...and now that the sevlet engine provides objects of these interfaces...how come u r able to to use the methods of these interfaces...for r they not empty methods?..
example how r u able to make the sendRedirect() method of HttpServletResponse interface work...is this method not an empty method?
there r several interfaces...whose objects r being used and passed in this similar fashion....(for example there r many methods that return an enumeration...which is used as if it were an ordinary class that can be instantiated..and whose methods r non empty emthods)
please help me resolve this mystery
sheeba

Answer 1

Don't call me "u". The word is "you". Likewise "are" and not "r".
The servlet engine creates objects of concrete classes that implement those interfaces. If you want to find the names of those classes in your particular server, you could use for examplereq.getClass().getName()