Java Exception throw your own exception

public class Main {
   static Object chatServer = null;

   public static void main(String[] args) {
      try {//  w w w  . j a v  a  2  s  .  c  o m
         sendChat("Hello, how are you?");
      } catch (ConnectionUnavailableException e) {
         System.out.println("Got a connection unavailable Exception!");
      }

      disconnectChatServer(chatServer);
   }

   private static void disconnectChatServer(Object chatServer) {
      if (chatServer == null)
         throw new IllegalChatServerException("Chat server is empty");
   }

   private static void sendChat(String chatMessage) throws ConnectionUnavailableException {
      if (chatServer == null)
         throw new ConnectionUnavailableException("Can't find the chat server");
   }

}

class ConnectionUnavailableException extends Exception {
   ConnectionUnavailableException(String message) {
      super(message);
   }
}

class IllegalChatServerException extends RuntimeException {
   IllegalChatServerException(String message) {
      super(message);
   }
}