Question

How it is possible to create object for HttpServletRequest Interface?

HttpServletRequest is an interface, but still servlet container can create object of the same. How? Why?

Answer 1

The servlet container has a class implementing this interface, and instantiates an object of this class. Just like when you do

List<String> list = new ArrayList<String>();

List is an interface, and you instantiate ArrayList, which is a class implementing List.

The servlet container does something like the following:

HttpServletRequest request = new TomcatHttpServletRequestImpl();

This is the basis of OO and polymorphism.