Why can't I seem to grasp interfaces?

Question

Could someone please demystify interfaces for me or point me to some good examples? I keep seeing interfaces popup here and there, but I haven't ever really been exposed to good explanations of interfaces or when to use them. I am talking about interfaces in a context of interfaces vs. abstract classes. JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

Interfaces allow you to program against a "description" instead of a type, which allows you to more-loosely associate elements of your software. Think of it this way: You want to share data with someone in the cube next to you, so you pull out your flash stick and copy/paste. You walk next door and the guy says "is that USB?" and you say yes - all set. It doesn't matter the size of the flash stick, nor the maker - all that matters is that it's USB. In the same way, interfaces allow you to generisize your development. Using another analogy - imagine you wanted to create an application that virtually painted cars. You might have a signature like this: public void Paint(Car car, System.Drawing.Color color)... This would work until your client said "now I want to paint trucks" so you could do this: public void Paint (Vehicle vehicle, System.Drawing.Color color)... this would broaden your app... until your client said "now I want to paint houses!" What you could have done from the very beginning is created an interface: public interface IPaintable{ void Paint(System.Drawing.Color color); } ...and passed that to your routine: public void Paint(IPaintable item, System.Drawing.Color color){ item.Paint(color); } Hopefully this makes sense - it's a pretty simplistic explanation but hopefully gets to the heart of it.