Scene inside of JFrame

Hi all!! I have got a JAVA3D application that I show it in a JFrame.
So, everything is correct.

--->This schem is correct:

class program3D extends JFrame{

public program3D(){   }

public BranchGroup createSceneGraph(){  }

public static void main ( String arg[] )
{
 new program3D();
}
}

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The problem is when I want to draw the scene inside of JPanel, and
then, this JPanel put inside of JFrame.

--->THE PROBLEM:The scene is not seen !!!

class program3D extends JPanel{

public program3D(){   }

public BranchGroup createSceneGraph(){  }

public static void main ( String arg[] )
{
     JFrame window=new JFrame("Main");
     window.setLayout( new BorderLayout() );
     window.getContentPane().add( new program3D(),
BorderLayout.CENTER); //PROBLEM

     window.setSize(500,500);
     window.setVisible(true);
}
}

Regards!