Interface vs abstract class vs concrete class in java

Interface vs abstract class vs concrete class:-

Interface:-

If we don’t know anything about implementation just we have requirement specification then we should go for interface.

Ex:-  Servlet, Collection

Abstract class:-

If we are taking about implementation but not completely (partial implementation) then we should go for abstract class.

Ex:-

 GenericServlet (AC), HTTPServlet (AC)

Concrete class:-

If we are taking about implementation completely and ready to provide service then we should go for concrete class.

Ex:-