Fetch restaurant list at a user's default address using Retrofit

RestaurantDataSource.java

/**
 * Fetch the current user's default address 
 */
public void getUserInfo(int userId) {
  ddApi.getUserInfo(userId, new Callback<User>() {
    @Override
    public void onResponse(@NonNull Call<User> call,
                 @NonNull Response<User> response) {
      if (response.isSuccessful() && response.body() != null) {
        User user = response.body();
        getRestaurants(user.defaultAddress.lat, user.defaultAddress.lng);
      } else {
        // display the error message contained in response.errorBody()
      }
    }

    @Override
    public void onFailure(@NonNull Call<User> call, @NonNull Throwable t) {
      // display a network error message
    }
  });
}

/**
 * Fetch restaurants at the given location
 */
public void getRestaurants(double lat, double lng) {
  ddApi.getRestaurants(lat, lng, new Callback<List<Restaurant>>() {
    @Override
    public void onResponse(@NonNull Call<List<Restaurant>> call,
                 @NonNull Response<List<Restaurant>> response) {
      if (response.isSuccessful() && response.body() != null) {
        // update adapter with restaurants
      } else {
        // display the error message contained in response.errorBody()
      }
    }

    @Override
    public void onFailure(@NonNull Call<List<Restaurant>> call, @NonNull Throwable t) {
      // display a network error message
    }
  });
}