void getAllCountries(@NonNull final SelectCountryCallback callback, String username){
	// Attempt to get countries from local cache, if present
  if(dbData(callback)) return;

	// Call API to get updated list of countries
	callToApi(callback,username);
}

void callToApi(callback,username);
{
  apiService.getCountries(username).enqueue(new Callback<CountriesResponse>() {
		@Override
		public void onResponse(final Call<CountriesResponse> call, final Response<CountriesResponse> response) {
			if (response.isSuccessful()){
				saveToDBAndCall(callback,response)
			} else {
				callback.onCountriesLoadFailed(new Throwable("An error occured while loading countries"));
			}
		}

		@Override
		public void onFailure(Call<CountriesResponse> call, Throwable t) {
			callback.onCountriesLoadFailed(t);
		}
	});
}

void dbData(callback){
 	RealmResults<Country> countries = realm.where(Country.class).findAll();
	if (!countries.isEmpty()){
		callback.onCountriesLoaded(countries);
    return true;
	}
  return false;
}

void saveToDBAndReturn(callback,response)
{
  realm.executeTransaction(new Realm.Transaction() {
					@Override
					public void execute(Realm realm) {
						if (response.isSuccessful()){
							realm.copyToRealmOrUpdate(response.body().countries);
							callback.onCountriesLoaded(response.body().countries);
						}
					}
				});
}