加入并退出Java中的课程子类

Question

我有一个包含两个子类的抽象类课程。

我需要实现加入/删除方法，这些方法基本上是从在线课程或大学课程分配或辞职的学生。

我如何从课程中实现抽象的join / drop方法两个子类？

然后在“学生课堂”中，我可以在大学/在线课程中创建一个新主题，然后将其返回。

感谢您的帮助，这是我的代码：

---

课程

public abstract class Course {

public String title;
public String description;
public LocalDate examDate;
public List<Lecture> lectures;

public abstract Course join();
public abstract Course drop();
}

class OnlineCourse extends Course{
public URL livestreamUrl;
public Course join() {

    System.out.println("joined the online course");
}
public Course drop() {

    System.out.println("dropped out of the online course");
}
}

class UniversityCourse extends Course{
public String roomName;
public Course join() {

    System.out.println("joined the university-course");
}
public Course drop() {

    System.out.println("dropped out of the university-course");
}
}

---

班级学生

public class Student {

public String matriculationNumber;
public String name;
public int age;

public Course study() {

    // TODO 4: Comment the code below back in
    // Change the Course type to OnlineCourse and set its title to "EIST"
    // return the new course    

    // Course course = new Course();
    // course.join();
    // return course;
    UniversityCourse EIST = new UniversityCourse(); 
    EIST.join();
    return EIST;
}
}

---

Answer 1

您可以在课程中添加学生的list，并在加入/删除过程中添加/删除像这样：

    public abstract class Course {

        public String title;
        public String description;
        public LocalDate examDate;
        public List<Lecture> lectures;
        protected List<Student> students;

        public Course(){
            // init
            // ...
            students = new ArrayList<>();
        }

        public abstract void join(Student student);

        public abstract void drop(Student student);
    }

    class OnlineCourse extends Course {
        public URL livestreamUrl;

        public void join(Student student) {
            students.add(student);
            System.out.println("joined the online course");
        }

        public void drop(Student student) {
            students.remove(student);
            System.out.println("dropped out of the online course");
        }
    }

    class UniversityCourse extends Course {
        public String roomName;

        public void join(Student student) {
            students.add(student);
            System.out.println("joined the university-course");
        }

        public void drop(Student student) {
            students.remove(student);
            System.out.println("dropped out of the university-course");
        }
    }