Fetch restaurant list using Retrofit

RestaurantDataSource.java

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
    }
  });
}