[vsareto]

That's pretty typical in C# land (another is service->repo->data access with DI/interfaces for each). Very likely the dev had that pattern down as a reflex. There was no consideration on their part because they already knew a solution that worked. They could move on to the other problems or requirements.

As another poster elsewhere said, the annoying thing is only the single implementation for the interfaces, and no real code that makes use of the abstraction. It only really alleviates other devs from asking "where are the interfaces for these classes?"

[malka]

Using an interface forces one to think about a clean API, that does not rely on internals.

[imtringued]

That doesn't make any sense. Java already has private and public as modifiers. The only meaningful difference is that interfaces prevent you from using private. That's such a shallow benefit. If you have the discipline to create interfaces you also have the discipline to use the right modifiers. The reality is that all those interfaces will just mirror the class and cause extra friction even though polymorphism is never needed.

[lmz]

In theory. Sometimes it only has one implementation and the details leak through.