to extend or not

From: - (nobody_at_hoem.om)
Date: 03/29/05 

Date: Tue, 29 Mar 2005 16:35:54 +0800

which is the preferred style?

public class App {

     private JFrame frame;

     public App() {
         frame = new JFrame();
     }
}

or

public class AppFrame extends JFrame {

     public AppFrame() {
     }
}