Exit_on_close

src/main/java/Notizbuch.java

@@ -19,6 +19,7 @@ public class Notizbuch extends JFrame implements ActionListener {
 	public Notizbuch() {
 		setTitle("Notizbuch");
 		setSize(400, 300);
+		setDefaultCloseOperation(EXIT_ON_CLOSE);
 	}
 
 	@Override