Should every single object have an interface and all objects loosely coupled?

Question

From what I have read best practice is to have classes based on an interface and loosely couple the objects, in order to help code re-use and unit test.

Is this corr

Answer 1

I'd only use interfaces where that level of abstraction was required - i.e. you need to use polymorphic behaviour. Common examples would be dependency injection or where you have a factory-type scenario going on somewhere, or you need to establish a "multiple inheritance" type behaviour.

In my case, with my development style, this is quite often (I favour aggregation over deep inheritance hierarchies for most things other than UI controls), but I have seen perfectly fine apps that use very little. It all depends...

Oh yes, and if you do go heavily into interfaces - beware web services. If you need to expose your object methods via a web service they can't really return or take interface types, only concrete types (unless you are going to hand-write all your own serialization/deserialization). Yes, that has bitten me big time...