public class EmailFragment extends Fragment {
    EmailCreated activity;

    public interface EmailCreated {
        String onEmailCreated(Bundle emailBundle);
    }

    public EditText subjectLineFrag, emailFrag;
    public String emails, subject;
    public Button confirmFrag;
    public Bundle emailBundle;

    @Nullable
    @org.jetbrains.annotations.Nullable
    @Override
    public View onCreateView(@NonNull @NotNull LayoutInflater inflater, @Nullable @org.jetbrains.annotations.Nullable ViewGroup container, @Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.email_fragment, container, false);
        emailFrag = view.findViewById(R.id.emailFrag);
        subjectLineFrag = view.findViewById(R.id.subjectLineFrag);
        confirmFrag = view.findViewById(R.id.confirmFrag);

        return view;
    }

    public Bundle storeEmail(View v, EditText subjectLineFrag, EditText emailFrag) {
        String emails = emailFrag.getText().toString();
        String subject = subjectLineFrag.getText().toString();
        emailBundle.putString("message", emails);
        emailBundle.putString("subject", subject);
        return emailBundle;
    }
   
    @Override
    public void onAttach(@NonNull @NotNull Context context) {
        //context will refer to the attached activity
        super.onAttach(context);
        activity = (EmailCreated) context;
    }

    @Override
    public void onCreate(@Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }


    //Implement Fragment Lifecycle
    @Override
    public void onStart() {
        super.onStart();
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
    }

    @Override
    public void onStop() {
        super.onStop();
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

    @Override
    public void onAttach(@NonNull @NotNull Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

public class GuestActivity2 extends AppCompatActivity implements EmailFragment.EmailCreated {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_guest2);

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.container, new EmailFragment());
        transaction.commit();
    }

    @Override
    public String onEmailCreated(Bundle emailBundle) {

        return null;
    }
}