public class ChatClient {
  public static void main(String[] args) {
    ChatMediator mediator = new ChatMediatorImpl();
    User user1 = new UserImpl(mediator, "Pankaj");
    User user2 = new UserImpl(mediator, "Lisa"); 
    User user3 = new UserImpl(mediator, "Saurabh");
    User user4 = new UserImpl(mediator, "David");
    mediator.addUser(user1);
    mediator.addUser(user2);
    mediator.addUser(user3);
    mediator.addUser(user4);
    user1.send("Hi All");
   }
}