title: Exception in thread "Thread-0" java.lang.NoClassDefFoundError: Server$WorkerThread
body: <p>My chat program was working fine in my system when i changed the IP and compiled in my system. Then I copied the class file into another and it worked fine in that system, too. However, when the client sends a message it gives the following error : </p>
  
  <p><code>Exception in thread "Thread-0" java.lang.NoClassDefFoundError: Server$WorkerThread</code></p>
  
  <p>I am using Windows 7. What can be wrong? </p>