Image Comparison between interfaces and abstract classes

1. Planes fly and birds fly. They all inherit the same interface "fly", but airplanes are the abstract class of F22 and birds are the abstract class of pigeons.
2. just like all doors (abstract class), I can't give you a door (I can't instantiate it), but I can give you a specific door or wooden door (polymorphism ); it can only be a door. You cannot say it is a window (single inheritance); a door can have a lock (Interface) or a doorbell (multiple implementations ). A door (abstract class) defines what you are and an interface (LOCK) specifies what you can do (one interface is best to do only one thing, you cannot require the lock to make sound (interface pollution )).