How to choose from two interfaces the one you need according to the condition?

Question

Java

Good afternoon!
Direct your thoughts to the right side, I can not solve the problem.
The application has 2 interfaces Api and ApiDemo. As the name implies, one works with a working server, the other with a demo one. When the application is launched, the user can test it in demo mode (there is a separate button for this).
I use Retrofit 2 to work with the server, and the worker api object is created like this
Api = new Retrofit.Builder()
.baseUrl(serverAddress + "/")
.addConverterFactory(GsonConverterFactory.create())
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.client(okHttpClient)
.build().create(Api.Class);
App.getApi
().auth(userName, password) is called.
A demo api can be created similarly in theory.
I save the "demo mode" flag in SharedPreference.
My problem is that I don't understand how to connect 2 different interfaces into one?
I want that when calling App.getApi () - I immediately return the desired interface (working or demo).
Otherwise, you will have to cut the heap when, and add an if-else condition everywhere with a check of the current mode of operation ... but you don’t want to.
Maybe I made a mistake with the architecture initially?

Answer 1

In theory, the API is what the interface is for, that for sale and test should not differ externally. That is, the interface itself must be one. And just baseUrl should differ.