Why Java Codegen Plugin prefer extends than implements?

[Wang Tao]

When I use implements I can define gRPC service as a spring bean easily, extends not friendly enough to my spring based app. 

Now I generate my codes with option 'enable_deprecated', this option will be deleted in the future?

[Carl Mastrangelo]

We extend because it allows us to evolve the API without breaking people.  If it was an interface we would never be able to add any more methods ever.  This is needed for backwards compatibility.

It will be removed, you should work on avoiding use of the interfaces to not be broken in the future.