fenetre en jbuilder

Réponse acceptée !
Salut,
Voici la methode:
 Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension frameSize =fenêtre.getSize();
    if (frameSize.height > screenSize.height) {
      frameSize.height = screenSize.height;
    }
    if (frameSize.width > screenSize.width) {
      frameSize.width = screenSize.width;
    }
    fenêtre.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
    fenêtre.setVisible(true);

Bonne chance.