ISP – effective interfaces
In this section, we will look at a principle that helps us write effective interfaces. It is known as ISP.
ISP advises us to keep our interfaces small and dedicated to achieving a single responsibility. By small interfaces, we mean having as few methods as possible on any single interface. These methods should all relate to some common theme.
We can see that this principle is really just SRP in another form. We are saying that an effective interface should describe a single responsibility. It should cover one abstraction, not several. The methods on the interface should strongly relate to each other and also to that single abstraction.
If we need more abstractions, then we use more interfaces. We keep each abstraction in its own separate interface, which is where the term interface segregation comes from —we keep different abstractions apart.
The related code smell to this is a large interface that covers several different topics...
