Remove the 'i' from your interfaces


Let’s say I’m creating two classes - A and B, when A is using B.

Because I don’t want A to be coupled to B, I’am injecting an interface that B implements.

Until today, even if I had only one implementation for this interface, I created an interface called IB, implement it in B and inject it to A.

The idea of creating an interface just to allow me to change the implementation of B in the future always felt like violation of YAGNI.

Well, yesterday I reached the “Interfaces and implementations” section in Clean Code of Uncle Bob.

He recommends to prevent from adding an I to interface name because the client (who uses the implementation) shouldn’t know that he’s getting an interface:

I prefer to leave interfaces unadorned. The preceding I, so common in today’s legacy wads, is a distraction at best and too much information at worst. I don’t want my users knowing that I’m handing them an interface…. So if I must encode either the interface or the implementation, I choose the implementation.

Then I thought about the fact that there are many classes in Java libraries that don’t starts with an ‘I’ although they are an interfaces: CharSequence , Connection etc.

So, I have decided to stop adding the ‘I’ prefix to my interfaces. This way I can create a single implementation and extract an interface in the future if I’ll need it.

Written on January 3, 2012