Need help to this Java problem.

Objectives:

To practice more with collections and exceptions.

Assignment:

Your job is to extend the Registration System we built in class (attached below) in 3 ways:

• Support a new type of class called a OpenUniversity student. These students do not have an ID, but they do have a phone number. Two students are the same if they have the same name and phone number.

• Allow each course to have a set of Open University students, in addition to regular students. There should be 2 capacities for each course, the number of regular students and the number of Open University students.

• The number of Open Unversity students should not exceed the number of regular students at any time or else an exception should be thrown.

• It should be possible to delete students from a course using a new "ds" command. When that command is entered, the system should ask the user for the ID of the student and then search both the full time students and Open University student lists for that student in the course. If found, that student should be removed from that list.

Retristration System: package mar06registration; import java.util.HashMap; import java.util.Map; import java.util.Scanner; public class RegistrationSystem { private Map school; public RegistrationSystem() { school = new HashMap(); } private static void out(String s) { System.out.print(s); } private static void outln(String s) { System.out.println(s); } public static void main(String[] args) { RegistrationSystem rs = new RegistrationSystem(); Scanner s = new Scanner(System.in); boolean done = false; do { out("What next? "); try { String cmd = s.next(); s.nextLine(); switch (cmd) { case "q": { done = true; outln("Goodbye!"); break; } case "ac": { handleAddCourse(s, rs); break; } case "as": { handleAddStudent(s, rs); break; } default: outln("I do not understand you!"); break; } } catch (Exception e) { outln("ERROR: "+e.getMessage()); } } while (!done); } private static void handleAddStudent(Scanner s, RegistrationSystem rs) { out("Student name: "); String name = s.next(); s.nextLine(); out("Student ID: "); String id = s.next(); s.nextLine(); out("Course: "); String courseName = s.next(); s.nextLine(); Student student = new Student(name, id); Course course = new Course(courseName); rs.addStudentToCourse(student, course); outln("Student added!"); } private static void handleAddCourse(Scanner s, RegistrationSystem rs) { out("Course name: "); String name = s.next(); s.nextLine(); out("Course capacity: "); int capacity = s.nextInt(); s.nextLine(); Course c = new Course(name, capacity); rs.addCourse(c); outln("Course added"); } private void addCourse(Course c) { if (courseExist(c)) { throw new RuntimeException("Course already exists"); } addCourseToSchool(c); } private boolean courseExist(Course c) { return school.get(c.getName()) != null; } private void addCourseToSchool(Course c) { school.put(c.getName(), c); } private void addStudentToCourse(Student student, Course course) { Course c = school.get(course.getName()); if (c == null) { throw new RuntimeException("No such course!"); } c.addStudent(student); } }