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Using interface reference variable without instantiation

Fei Wong
Greenhorn

Joined: Jun 15, 2009
Posts: 11
Hi all, I have a question on the servlet. The code is in below



May I know why the HttpServletResponse interface reference variable can straight using the method without instantiation? Thanks
Charles 'King
Ranch Hand

Joined: Jul 05, 2009
Posts: 56


Servlets are controlled by the container. The container handles creating request and response objects. The container creates a thread for each request and calls the service method; passing request and response objects as arguments. Go to Sun's site and read about the servlet life cycle. If you have questions on passing objects to methods, please google it.
Mark E Hansen
Ranch Hand

Joined: Apr 01, 2009
Posts: 650
To say this differently, the container created a response object which implements the HttpServletResponse interface. All your code has to know is how to call the methods described by the interface. You don't need to know anything about how the container actually implemented them.
Jinglong Wang
Greenhorn

Joined: Mar 05, 2010
Posts: 12
Just like this..
I have a interface..

And then, I create a class implement InterfaceDemo interface.

last i test it.

Result:


we can see,the console print two lines.

this is just like the servlet, when the containner startup, it can create the servlet instance, than run the HttpServlet service method, it didn't know what the implements is.Just run the interface methods...
 
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