L-ectron-X hat gesagt.:
setLocationRelativeTo(null);
Dimension d = this.getToolkit().getScreenSize(); this.setLocation((int) ((d.getWidth() - this.getWidth()) / 2), (int) ((d.getHeight() - this.getHeight()) / 2));
[PS: Wer fragen will, ob ich gegoogelt habe, ich HABE ES!]
public static void fensterZentrieren(JFrame fenster) {
Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
int x = dimension.width;
int y = dimension.height;
int fensterX = (x - fenster.getWidth()) / 2;
int fensterY = (y - fenster.getHeight()) / 2;
fenster.setLocation(fensterX, fensterY);
}