Refactor: open window in the center

src/main/java/ChatClient.java

@@ -46,6 +46,7 @@ public class ChatClient extends JFrame implements KeyListener {
         setVisible(true);
         setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
         setDefaultCloseOperation(EXIT_ON_CLOSE);
+        setLocationRelativeTo(null);
     }
     private void receiveMessages() {
         try {