public class Enrolment {

    private List<Session> sessions;

    public Enrolment() {
        this.sessions = new ArrayList<>();
    }

    public addSession(Session session) {
        this.sessions.add(session);
    }
}

public class Session {

    private int time;

    public Session(int time) {
        this.time = time;
    }
}

public class Lecture extends Session {

    private String lecturer;

    public Lecture(int time, String lecturer) {
        super(time);
        this.lecturer = lecturer;
    }
}

public class Tutorial extends Session {

    private String tutor;

    public Tutorial(int time, String tutor) {
        super(time);
        this.tutor = tutor;
    }

}

public class test {
    public static void main(String[] args) {
        Enrolment newEnrolment = new Enrolment();

        Lecture morningLec = new Lecture(900, "Dr. Mike");
        newEnrolment.addSession(morningLec);

        Tutorial afternoonTut = new Tutorial(1400, "John Smith");
        newEnrolment.addSession(afternoonTut);

        Lecture middayLec = new Lecture(1200, "Mr. Micheals");
        newEnrolment.addSession(middayLec);

        Tutorial NightTut = new Tutorial(1900, "Harry Pauls");
        newEnrolment.addSession(NightTut);
    }
}