I have doubt in the marker interface. What is marker interface? If the interface is not having any methods, then it said to be marker inetface?. What is advantage of using marker interface?
I also recommend that when feeling the urge to ask "what is a...?" that your first response should be to use a suitable search engine. Chances are good that someone has already published a very good definition of the term in question. You will save yourself the time of waiting for a response, and the time of others from repeating information that already exists elsewhere.
Good luck!
Don't get me started about those stupid light bulbs.