How to use app Update Manager in main activity

Question

I am trying to implement app Update Manager for an immediate type. I referred to the 3rd answer of this question How to work with Android's in-app update API? but I don't think I understood how exactly the code should be used. This is how I did my coding

 private AppUpdateManager appUpdateManager;
 int REQUEST_APP_UPDATE;
 setContentView(R.layout.activity_starternew);
appUpdateManager =AppUpdateManagerFactory.create(Starternew.this);
appUpdateManager
        .getAppUpdateInfo()
        .addOnSuccessListener(
                appUpdateInfo -> {
                    if ((appUpdateInfo.updateAvailability() == UpdateAvailability.UPDATE_AVAILABLE) && appUpdateInfo.isUpdateTypeAllowed(AppUpdateType.IMMEDIATE)) {
                        try {
                            appUpdateManager.startUpdateFlowForResult(
                                    appUpdateInfo,
                                    AppUpdateType.IMMEDIATE,
                                    this,
                                    REQUEST_APP_UPDATE);
                        } catch (IntentSender.SendIntentException e) {
                            e.printStackTrace();
                        }
                    }
                //}
});

Below is the onresume method

 @Override
protected onResume(){
super.onResume();
appUpdateManager
        .getAppUpdateInfo()
        .addOnSuccessListener(
                appUpdateInfo ->{
                    if (appUpdateInfo.updateAvailability()==UpdateAvailability.DEVELOPER_TRIGGERED_UPDATE_IN_PROGRESS){
                        try {
                            appUpdateManager.startUpdateFlowForResult(
                                    appUpdateInfo,
                                    AppUpdateType.IMMEDIATE,
                                    this,
                                    REQUEST_APP_UPDATE
                            );
                        }catch (IntentSender.SendIntentException e){
                            e.printStackTrace();
                        }
                    }
                });

       // )
}}

When I use the above I get error message, onresume is supposed to have a return, and method does not override method from its superclass. This is the first time I am using this api, I read the documentation but am not quite sure if my code asides from the onresume method is correct, and how do I handle the current errors in the onresume method? Or could someone please direct me to a full example in java of how to test it Please help. The on resume method comes at the very end of the code for main activity.