How to getSharedPreferences in Application?

I tried to call getSharedPreferences in Application...

public class App extends Application{
    public App() {
        SharedPreferences prefs = getSharedPreferences(SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE);
    }
}

...but I got a NullPointerException:

java.lang.NullPointerException: Attempt to invoke virtual method
  'android.content.SharedPreferences
  android.content.Context.getSharedPreferences(java.lang.String, int)' 
  on a null object reference

I also tried this and got same exception:

Context con = getApplicationContext();

How can I call getSharedPreferences?

Override onCreate(), in your app,

@Override
public void onCreate() {
    super.onCreate();

and do it there. Don't forget to declare your Application subclass in the AndroidManifest as well. E.g.

  <application
        android:name="App"