No me aparecen los botones, duda de swing basico

[Fuzzylog]

De la web de sun.

Painting in Swing
Swing starts with AWT's basic painting model and extends it further in order to maximize performance and improve extensibility. Like AWT, Swing supports the paint callback and the use of repaint() to trigger updates. Additionally, Swing provides built-in support for double-buffering as well as changes to support Swing's additional structure (like borders and the UI delegate). And finally, Swing provides the RepaintManager API for those programs who want to customize the paint mechanism further.

Vamos, que a veces no funciona si no usas el método repaint().