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

Not really. Service components (class that do things for your application) are a good fit for interfaces, but as a rule I wouldn't bother having interfaces for, say, basic entity classes.

For example: If you're working on a domain model, then that model shouldn't be interfaces. However if that domain model wants to call service classes (like data access, operating system functions etc) then you should be looking at interfaces for those components. This reduces coupling between the classes and means it's the interface, or "contract" that is coupled.

In this situation you then start to find it much easier to write unit tests (because you can have stubs/mocks/fakes for database access etc) and can use IoC to swap components without recompiling your applications.