Why use interfaces?

[fenix793]

I have been reading up on interfaces mostly from the series of articles about interfaces at DevShed After reading the article I think I am even more confused about interfaces. The author uses an interface to build a page generator but it seems really unnecessary. What is the point of interfaces? When should I be using them? Can someone provide an example of when I would have to use an interface? I feel like the examples I'm seeing are using interfaces just for the sake of using them.

Thanks all

[NogDog]

I personally have not had much - if any - reason to use interfaces in the PHP apps I've worked on so far. My OOP code normally depends on abstract classes rather than interfaces in order to generalize object types.

The only reason I see to use an interface is when you need that "contract" established that a given class will have a particular set of methods, allowing you to use type-hinting in another class to guarantee that a supplied object parameter will fulfill that contract. I guess nothing I've worked on so far has been complicated enough that I needed interfaces to provide those contracts, as abstract classes have been sufficient for that so far.