使用这些类有问题吗？这个静态接口以后会不会给应用程序类带来任何问题？

public class App extends Application {
private static KareezAPI apiService;
private InternetConnectionListener mInternetConnectionListener;
public static final int DISK_CACHE_SIZE = 10 * 1024 * 1024; // 10 MB
public void setInternetConnectionListener(InternetConnectionListener listener) {
    mInternetConnectionListener = listener;
}

public void removeInternetConnectionListener() {
    mInternetConnectionListener = null;
}

public KareezAPI getApiService(Activity activity) {
    if (apiService == null) {
        apiService = provideRetrofit(KareezAPI.BASE_URL,activity).create(KareezAPI.class);
        }
    return apiService;
}
                                   }

这是接口：

public interface KareezAPI{
String BASE_URL="https://baseurl.heroapp.com/";
@POST("register")
Call<RegisterResponse> RegisterUser( @Body RegisterData registerData);

@POST("login")
Call<RegisterResponse> LoginUser(@Body LoginData loginData); public interface LoginUserCallback{
    public void onResponse(Call<RegisterResponse> call, Response<RegisterResponse> response);
    public void onFailure(Call<RegisterResponse> call, Throwable t);
}

}

这就是这个接口和app类的用法

((App) activity.getApplication()).getApiService(activity).LoginUser(loginData).enqueue(new 
                                               Callback<RegisterResponse>() {
        @Override
        public void onResponse(@NonNull Call<RegisterResponse> call, @NonNull 
             Response<RegisterResponse> response) {
            loginUserCallback.onResponse(call, response);
        }

        @Override
        public void onFailure(@NonNull Call<RegisterResponse> call, Throwable t) {
            loginUserCallback.onFailure(call, t);
        }
    });