setVisible

src/main/java/Notizbuch.java

@@ -68,6 +68,7 @@ public class Notizbuch extends JFrame implements ActionListener {
 	public static void main(String[] args) {
 		 SwingUtilities.invokeLater(() -> {
 			  Notizbuch notizbuch = new Notizbuch();
+			  notizbuch.setVisible(true);
 		 });	
 	}
 }