用java写一个学生选课系统的代码

好的，我可以为您提供一个学生选课系统的Java代码示例。

代码如下：

import java.util.ArrayList;

class Student {
    private String name;
    private int id;
    private ArrayList<Course> courses;

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

    public String getName() {
        return name;
    }

    public int getId() {
        return id;
    }

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

    public void enroll(Course course) {
        courses.add(course);
    }

    public void drop(Course course) {
        courses.remove(course);
    }
}

class Course {
    private String name;
    private int id;
    private ArrayList<Student> students;
    private int maxStudents;

    public Course(String name, int id, int maxStudents) {
        this.name = name;
        this.id = id;
        this.students = new ArrayList<>();
        this.maxStudents = maxStudents;
    }

    public String getName() {
        return name;
    }

    public int getId() {
        return id;
    }

    public ArrayList<Student> getStudents() {
        return students;
    }

    public int getMaxStudents() {
        return maxStudents;
    }

    public boolean addStudent(Student student) {
        if (students.size() < maxStudents) {
            students.add(student);
            return true;
        } else {
            return false;
        }
    }

    public void removeStudent(Student student) {
        students.remove(student);
    }
}

public class Main {
    public static void main(String[] args) {
        Course course1 = new Course("Math", 101, 3);
        Course course2 = new Course("Science", 102, 2);

        Student student1 = new Student("John", 1);
        Student student2 = new Student("Sarah", 2);
        Student student3 = new Student("Tom", 3);

        course1.addStudent(student1);
        course1.addStudent(student2);
        course1.addStudent(student3);
        course2.addStudent(student1);
        course2.addStudent(student2);

        System.out.println("Students enrolled in " + course1.getName() + ":");
        for (Student student : course1.getStudents()) {
            System.out.println(student.getName());
        }

        System.out.println("Students enrolled in " + course2.getName() + ":");
        for (Student student : course2.getStudents()) {
            System.out.println(student.getName());
        }

        student1.enroll(course1);
        student1.enroll(course2);

        System.out.println("Courses enrolled by " + student1.getName() + ":");
        for (Course course : student1.getCourses()) {
            System.out.println(course.getName());
        }

        student1.drop(course1);

        System.out.println("Courses enrolled by " + student1.getName() + " after dropping " + course1.getName() + ":");
        for (Course course : student1.getCourses()) {
            System.out.println(course.getName());
        }

        course1.removeStudent(student1);

        System.out.println("Students enrolled in " + course1.getName() + " after removing " + student1.getName() + ":");
        for (Student student : course1.getStudents()) {
            System.out.println(student.getName());
        }
    }
}

以上程序可以实现学生选课系统的基本功能，包括课程的添加和删除、学生的选课和退选等。如果您有任何疑问，请随时与我进行交流。