What is the purpose of Interfaces? IMHO, it's just a collection of properties, method and events which can be used over and over again by different classes.
It;s no different than declaring the needed method or property in the classes separately rather than using Interface (because in Interface, you have to write the inner working in each classes implementing the interface). Is there a case where an interface comes in handy (I mean cases where Interfaces are absolutely necessary, without them the program won't work)? thanks