Enforced duplication check on nickname change

src/main/java/ch/unibas/dmi/dbis/cs108/multiplayer/client/MessageFormatter.java

@@ -7,7 +7,7 @@ public class MessageFormatter {
    * handle it. May need to be redesigned one the games uses a GUI
    *
    * @param msg the Messaged to be reformatted
-   * @return the reformatted message
+   * @return the reformatted message in the form HEADR$msg
    */
 
   public static String formatMsg(String msg) {

src/main/java/ch/unibas/dmi/dbis/cs108/multiplayer/server/ClientHandler.java

@@ -99,9 +99,12 @@ public class ClientHandler implements Runnable {
   }
 
   public void changeUsername(String newName) {
-
+    if (AllClientNames.allNames("").contains(newName)) {
+      newName = NameGenerator.randomName(newName);
+    }
     String h = this.clientUserName; //just a friendly little helper
     this.clientUserName = newName;
+    AllClientNames.allNames(newName);
     broadcastMessage(h +" have changed their nickname to " + clientUserName);
   }