制作一个学生选课系统,系统包括学号,姓名,性别,年级,密码。课程要包括课程编号,课程名称,已选人数,可选人数,授课老师。文件CourseDB.java:单例类,模拟数据库中的课程,初始化后至少封装10门课程

是的，你说得完全正确。下面是一个简单的Java代码示例，可以实现你所需要的学生选课系统：

import java.util.ArrayList;
import java.util.List;

public class Student {
    private String id;
    private String name;
    private String gender;
    private int grade;
    private String password;
    private List<Course> courses;

    public Student(String id, String name, String gender, int grade, String password) {
        this.id = id;
        this.name = name;
        this.gender = gender;
        this.grade = grade;
        this.password = password;
        this.courses = new ArrayList<>();
    }

    public void selectCourse(Course course) {
        if (course.getAvailableSeats() > 0) {
            courses.add(course);
            course.addStudent();
        } else {
            System.out.println("This course is full.");
        }
    }

    public void dropCourse(Course course) {
        if (courses.contains(course)) {
            courses.remove(course);
            course.removeStudent();
        } else {
            System.out.println("You haven't selected this course.");
        }
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getGender() {
        return gender;
    }

    public int getGrade() {
        return grade;
    }

    public String getPassword() {
        return password;
    }

    public List<Course> getCourses() {
        return courses;
    }
}

class Course {
    private String id;
    private String name;
    private int selectedSeats;
    private int availableSeats;
    private String teacher;

    public Course(String id, String name, int availableSeats, String teacher) {
        this.id = id;
        this.name = name;
        this.selectedSeats = 0;
        this.availableSeats = availableSeats;
        this.teacher = teacher;
    }

    public void addStudent() {
        selectedSeats++;
        availableSeats--;
    }

    public void removeStudent() {
        selectedSeats--;
        availableSeats++;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getSelectedSeats() {
        return selectedSeats;
    }

    public int getAvailableSeats() {
        return availableSeats;
    }

    public String getTeacher() {
        return teacher;
    }
}

class CourseDB {
    private static CourseDB instance;
    private List<Course> courses;

    private CourseDB() {
        courses = new ArrayList<>();
        courses.add(new Course("001", "Math", 30, "Tom"));
        courses.add(new Course("002", "English", 50, "Jerry"));
        courses.add(new Course("003", "Computer Science", 20, "John"));
        courses.add(new Course("004", "Physics", 40, "Lucy"));
        courses.add(new Course("005", "Chemistry", 35, "Bob"));
        courses.add(new Course("006", "Biology", 25, "Lily"));
        courses.add(new Course("007", "History", 30, "David"));
        courses.add(new Course("008", "Geography", 30, "Frank"));
        courses.add(new Course("009", "Music", 15, "Mary"));
        courses.add(new Course("010", "Art", 20, "Kate"));
    }

    public static CourseDB getInstance() {
        if (instance == null) {
            instance = new CourseDB();
        }
        return instance;
    }

    public List<Course> getCourses() {
        return courses;
    }
}

public class Main {
    public static void main(String[] args) {
        CourseDB courseDB = CourseDB.getInstance();
        List<Course> courses = courseDB.getCourses();

        Student student1 = new Student("001", "Tom", "Male", 1, "123456");
        Student student2 = new Student("002", "Lucy", "Female", 2, "123456");

        System.out.println("Course List:");
        for (Course course : courses) {
            System.out.println(course.getId() + " " + course.getName() + " " + course.getTeacher() + " " + course.getAvailableSeats());
        }

        System.out.println("\nStudent 1 selects courses:");
        student1.selectCourse(courses.get(0));
        student1.selectCourse(courses.get(1));
        student1.selectCourse(courses.get(2));
        for (Course course : student1.getCourses()) {
            System.out.println(course.getId() + " " + course.getName() + " " + course.getTeacher());
        }

        System.out.println("\nStudent 2 selects courses:");
        student2.selectCourse(courses.get(2));
        student2.selectCourse(courses.get(3));
        for (Course course : student2.getCourses()) {
            System.out.println(course.getId() + " " + course.getName() + " " + course.getTeacher());
        }

        System.out.println("\nStudent 1 drops a course:");
        student1.dropCourse(courses.get(1));
        for (Course course : student1.getCourses()) {
            System.out.println(course.getId() + " " + course.getName() + " " + course.getTeacher());
        }
    }
}

上面的代码演示了如何创建一个名为CourseDB的单例类，模拟数据库中的课程。初始化后，它至少包含10门课程。此外，还定义了一个名为Student的类，表示学生，它拥有一些基本属性，如学号、姓名、性别、年级和密码，以及一个名为courses的列表来存储所选的课程。在Student类中定义了两个方法：selectCourse和dropCourse，用于选课和退课。最后，还定义了一个名为Course的类，表示课程，它拥有一些基本属性，如课程编号、课程名称、已选人数、可选人数和授课老师。

在主函数中，我们首先获取CourseDB中的所有课程，然后创建两个学生对象，分别选取一些课程，并演示了如何退课。