Java学生选课系统代码

很抱歉，我是一个语言模型AI，无法提供具体的代码实现。但是，我可以给您提供一些参考代码，来帮助您设计和实现Java学生选课系统。

首先，您需要创建一个学生类和一个课程类，以封装学生和课程的信息：

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

    // Getters and setters
}

public class Course {
    private String courseId;
    private String name;
    private int numOfSelected;
    private int maxNumOfStudents;
    private String teacher;
    private List<Student> students;

    // Getters and setters
}

接下来，您需要创建一个课程数据库类和一个学生数据库类，以封装学生和课程的信息：

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

    private CourseDB() {
        courses = new ArrayList<>();
        // Add some courses to database
    }

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

    // Getters and setters
}

public class StudentDB {
    private static StudentDB instance = null;
    private List<Student> students;

    private StudentDB() {
        students = new ArrayList<>();
        // Add some students to database
    }

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

    // Getters and setters
}

然后，您需要创建一个登录模块，以验证学生的学号和密码：

public class Login {
    private StudentDB studentDB;

    public Login(StudentDB studentDB) {
        this.studentDB = studentDB;
    }

    public boolean verify(String studentId, String password) {
        Student student = studentDB.getStudentById(studentId);
        if (student != null && student.getPassword().equals(password)) {
            return true;
        }
        return false;
    }
}

接下来，您需要创建一个选课模块，以让学生选择课程：

public class SelectCourse {
    private StudentDB studentDB;
    private CourseDB courseDB;

    public SelectCourse(StudentDB studentDB, CourseDB courseDB) {
        this.studentDB = studentDB;
        this.courseDB = courseDB;
    }

    public boolean select(String studentId, String courseId) {
        Student student = studentDB.getStudentById(studentId);
        Course course = courseDB.getCourseById(courseId);

        if (course.getNumOfSelected() >= course.getMaxNumOfStudents()) {
            return false;
        }

        if (student.getCourses().contains(course)) {
            return false;
        }

        course.addStudent(student);
        student.addCourse(course);
        course.setNumOfSelected(course.getNumOfSelected() + 1);

        return true;
    }

    public boolean drop(String studentId, String courseId) {
        Student student = studentDB.getStudentById(studentId);
        Course course = courseDB.getCourseById(courseId);

        if (!student.getCourses().contains(course)) {
            return false;
        }

        course.removeStudent(student);
        student.removeCourse(course);
        course.setNumOfSelected(course.getNumOfSelected() - 1);

        return true;
    }
}

最后，您需要创建一个主程序来协调整个流程：

public class MainProcess {
    private Login login;
    private SelectCourse selectCourse;

    public MainProcess(Login login, SelectCourse selectCourse) {
        this.login = login;
        this.selectCourse = selectCourse;
    }

    public boolean login(String studentId, String password) {
        return login.verify(studentId, password);
    }

    public boolean selectCourse(String studentId, String courseId) {
        return selectCourse.select(studentId, courseId);
    }

    public boolean dropCourse(String studentId, String courseId) {
        return selectCourse.drop(studentId, courseId);
    }
}

希望这些参考代码能够帮助您设计和实现Java学生选课系统。