Android Studio – Nothing shows up while calling a method

I was developing an exam score calculator app.
When I want to call AD methods,advertisements don’t show up.

Calculation process happens in OnCreate method:

public class resultActivity extends AppCompatActivity {
    public String responseId;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_result);
        /*Calculation...*/}

and other voids like:

public void requestAd() {
/*AD RQUESTING PROCESS...*/
}

and

 public void showAd() {
/*AD SHOWING PROCESS...*/
}

AD team gave me this code to call the method and it works well:

requestButton.setOnClickListener(v -> requestAd());
 showButton.setOnClickListener(v -> showAd());

But the Problem is I don’t have buttons to call them so I tried this:

public class resultActivity extends AppCompatActivity {
    public String responseId;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_result);
        requestAd();
        showAd();

        /*Calculation...*/}

But when the activity starts ads don’t show up!
The whole question is I want this methods to be called while this activity starts.
thank you.