public class Main {

    public static void main(String[] args) {

        EntranceSystem entrance = EntranceSystem.getInstance();

        Staff s1 = entrance.admit("Mr Black");
        Guest g1 = entrance.admit("Mr CHAN", s1); // name of guest and the staff he is to meet
        Staff s2 = entrance.admit("Mr White");
        Staff s3 = entrance.admit("Mr Brown");
        Guest g2 = entrance.admit("Mr LEE", s2);

        entrance.listPeople();

        /* The program gives 5 lines of output as follows:
                Mr Black 
                Mr CHAN (Guest of Mr Black) 
                Mr White
                Mr Brown
                Mr LEE (Guest of Mr White)        
        */

    }

}