How to make service class extends another class as well?

I'm going to read some data from server each time and then show them as notification to the user. So I have a class that extends Service and I also have another class that's called GetNotifications and ServiceClass uses it to do some functions.

this is my ServiceClass:

public class ServiceClass extends Service {

public Context context = this;

@Override
public IBinder onBind(Intent intent) {
    return null;
}

@Override
public void onCreate() {

    shared= PreferenceManager.getDefaultSharedPreferences(context);
    handler = new Handler();
    runnable = new Runnable() {
        public void run() {       
            boolean isregistered=Utils.Checking_Running_Service(shared);
            if (isregistered)
            {
                GetNotifications getNoti=new GetNotifications(context);
                getNoti.getNotificationRequest();
            }
            handler.postDelayed(runnable, 5000);
        }
    };
    handler.postDelayed(runnable, 1000);
}
}

and this is my GetNotifications class:

 public class GetNotifications extends MyActivity{
 Context mycontext;

 public GetNotifications(Context context){
   mycontext=context;
}

public void getNotificationRequest() {

    if (Utils.isOnline(mycontext)) {

        HashMap<String, String> hashMap = new HashMap<>();
        .
        .
        .
        WebServiceManager webServiceManager = new WebServiceManager(???, 0, "get");
        webServiceManager.execute(hashMapForWeb);
    }
}
}...//and some another functions for getting result from webservice

For some reasons I need to use a MyActivity context as input of WebServiceManager class.(where I used ??? above). actually I need to make MyActivity myactivity=this; and use myactivity as input of WebServiceManager class.but I get error that you cant call "this" before onCreate. I have to say I dont want to startActivity from my service class to GetNotification Activity.so if I even have onCreate,it wont call. (instead of using startActivity in service class I just want to call getNotificationRequest method as I wrote above.because if I use startActivity,it will show me a white page each time I send notification). So I think if my service class could extend MyActivity as well,I would use its context for my aim:|