diff --git a/src/main/java/ChatClient.java b/src/main/java/ChatClient.java
index f39bc2f..30b486c 100644
--- a/src/main/java/ChatClient.java
+++ b/src/main/java/ChatClient.java
@@ -7,7 +7,7 @@ import java.net.Socket;
 
 public class ChatClient extends JFrame implements KeyListener {
     private String address;
-    private int port;
+    private String connectionFailedMessage;
     private Socket connectionToServer;
     private BufferedReader fromServerReader;
     private PrintWriter toServerWriter;
@@ -17,12 +17,11 @@ public class ChatClient extends JFrame implements KeyListener {
     private JTextField inputTextField;
     private JScrollPane outputScrollPane;
 
-    public ChatClient(int port) {
+    public ChatClient() {
         super("Chat");
-        this.port = port;
         address = JOptionPane.showInputDialog("bitte IP-Adresse");
-        
-        if (address != null) {
+        if (null != address) {
+            connectionFailedMessage = "Verbindung zum Server " + (address.isEmpty() ? "" : ("\"" + address + "\"")) + " fehlgeschlagen.";
             receiveMessages();
         }
     }
@@ -42,14 +41,15 @@ public class ChatClient extends JFrame implements KeyListener {
         add(inputTextField, BorderLayout.SOUTH);
 
         setVisible(true);
-        setSize(800, 600);
+        setSize(Constants.WINDOW_WIDTH, Constants.WINDOW_HEIGHT);
         setDefaultCloseOperation(EXIT_ON_CLOSE);
+        setLocationRelativeTo(null);
     }
     private void receiveMessages() {
         try {
-            connectionToServer = new Socket(address, port);
-            fromServerReader = new BufferedReader(new InputStreamReader(connectionToServer.getInputStream()));
-            toServerWriter = new PrintWriter(new OutputStreamWriter(connectionToServer.getOutputStream()));
+            connectionToServer = new Socket(address, Constants.PORT);
+            fromServerReader   = new BufferedReader(new InputStreamReader(connectionToServer.getInputStream()));
+            toServerWriter     = new PrintWriter(new OutputStreamWriter(connectionToServer.getOutputStream()));
 
             initGui();
 
@@ -59,7 +59,7 @@ public class ChatClient extends JFrame implements KeyListener {
                 outputScrollPane.getVerticalScrollBar().setValue(outputScrollPane.getVerticalScrollBar().getMaximum());
             }
         } catch (IOException e) {
-            JOptionPane.showMessageDialog(null, "Verbindung zum Server \"" + address + "\" fehlgeschlagen.");
+            JOptionPane.showMessageDialog(null, connectionFailedMessage);
             dispose();
         } finally {
             if (null != connectionToServer) {
@@ -107,6 +107,6 @@ public class ChatClient extends JFrame implements KeyListener {
     }
 
     public static void main(String[] args) {
-        new ChatClient(3141);
+        new ChatClient();
     }
 }
diff --git a/src/main/java/Constants.java b/src/main/java/Constants.java
new file mode 100644
index 0000000..5848138
--- /dev/null
+++ b/src/main/java/Constants.java
@@ -0,0 +1,5 @@
+public class Constants {
+    public static final int WINDOW_WIDTH  = 800;
+    public static final int WINDOW_HEIGHT = 600;
+    public static final int PORT          = 3141;
+}