AppCompate Themes doesn't view day or night view 1

Android Programming (3rd Edition) 22. Styles and Themes
1

if I change the switch: MODE_NIGHT_YES to NO, nothing is changing in the app
I cannot find a sampe wirh the java Nerd 4 construction.
An InitApplication exist in the directory, but where should I implement folloeing lines to call the InitApplication?

Sample Code

Mainactivity
public class Activity_MindX extends SingleFragmentActivity
{
private final String LOG = this.getClass().getName();

@Override
protected Fragment createFragment() {
    return new FragmentMenuMindX();
}

Sample for an called Fragment

// ################################################
public void onCardSetUpdated(CardSet cardset) {
// ################################################
	FragmentManager fm = getSupportFragmentManager();
	fm.findFragmentById(R.id.fragmentContainer);
	}
@Override
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (InitApplication.getInstance().isNightModeEnabled()) {
        AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
    } else {
        AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
    }
    setContentView(R.layout.activity_main);


// ################################################
public void onCardSetUpdated(CardSet cardset) {

// ################################################
FragmentManager fm = getSupportFragmentManager();
fm.findFragmentById(R.id.fragmentContainer);
}

in the Fragment

public class FragmentMenuMindX extends Fragment implements OnClickListener,
OnChartValueSelectedListener,
SeekBar.OnSeekBarChangeListener,
MindXconstants, MessageConst, DialogConstants {

FragemtActivity

@TargetApi(11)
@Override
// ################################################
public View onCreateView(LayoutInflater inflater, ViewGroup parent,
	Bundle savedInstanceState) {
// ################################################
**AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);**
View v = inflater.inflate(R.layout.activity_menu_mind_x, parent, false