Question

I believe we invent things for some reasons: OOP came because procedural programming didn’t meet our needs; The same goes for the Interface, because other OOP features like Abstract didn’t meet our needs.

There are plenty of articles and guides written about what an Interface IS, CAN DO and HOW TO USE IT, however, I’m wondering what the actual philosophy behind the of creation of Interface is? Why we need to have Interface?

Answer 1

Conceptually, an interface is a contract. It’s a way of saying that anything implementing this interface is capable of doing these set of things.

Different languages have different things that interfaces can define, and different ways of defining them, but that concept remains.

Using interfaces allows you to not care how some particular task is completed; it allows you to just ensure that it is completed.

By allowing implementations to differ, and allowing the code to define just the smallest subset of what it needs, it allows you to generalize your code.

Perhaps you want to write a method to write a sequence of numbers on the screen. You don’t want to go around writing methods for doing that for an array, a set, a tree, on any of the (many) other commonly used data structures. You don’t need to care whether you’re dealing with an array or a linked list, you just need some way of getting a sequence of items. Interfaces allow you to define just the minimal set of what you need, lets say a getNextItem method, and then if all of those data structures implement that method and interface they can use the one generalized method. That’s much easier than writing a separate method for each type of data structure you want to use. (This isn’t the only use of interface, just a common one.)