title: Service and DAO always implement interfaces
body: <p>In all the MVC projects I've seen, "service" and "DAO" classes always implemented their own interfaces. But almost all the times, I haven't seen a situation in which having this interface has been useful.</p>
  
  <p>Is there any reason to use interfaces in these cases? What may be the consequence of not using interfaces in "service" and "DAO" classes? I can't imagine any consequences. </p>