public String get_user_courses_in_circle_by_year(int user_id, int year, int circle_id)
        {
                User user = get_user_by_id(user_id);
                
                if(user==null)
                        return "";

                ArrayList<Circle> circles=user.user_circles;
                ArrayList<Course> courses=user.user_courses;

                String user_courses="";
                
                for(Circle circle: circles) //for each circle in user circles
                {
                        if(circle.get_circle_year()==year && circle.get_circle_id()==circle_id) //if circle in year
                        {
                                for(Course course: courses)
                                {
                                        user_courses+=course.get_course_name() + "," + course.get_course_id() + ",";
                                }
                                
                                break;
                        }
                }
                
                if(!user_courses.isEmpty())
                                user_courses=user_courses.substring(0, user_courses.length() - 1); //remove last comma
                
                return user_courses;
        }