public static void main(String[] args) {
            //Liskov sub
            ProgrammingCourse[] courseList = { new AdvancedJavaCourse("Advanced Java","COURSE_NUMBER"),
            new IntroJavaCourse("Introduction to Java","COURSE_NUMBER"),
            new IntroToProgrammingCourse("Introduction to Programming","COURSE_NUMBER")};
        
            for(ProgrammingCourse c : courseList) {
                System.out.println(c.getCourseName());
        }
    }