Какие знаешь примеры реализации интерфейсов Spring Boot

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByEmail(String email);
}

public interface UserService {
    User createUser(UserDto userDto);
    User getUserById(Long id);
}

@RestController
@RequestMapping("/api/users")
public class UserController {
    @Autowired
    private UserService userService;
    
    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody UserDto userDto) {
        return ResponseEntity.ok(userService.createUser(userDto));
    }
}