dispose

src/main/java/ChatClient.java

@@ -60,6 +60,7 @@ public class ChatClient extends JFrame implements KeyListener {
         
         catch (Exception e) {
             JOptionPane.showMessageDialog(null, "Verbindung zum Server \"" + address + "\" fehlgeschlagen.");
+            dispose();
         }
         finally {
         	if (connectionToServer != null) {