java 学生选课系统实现： 1.系统至少应包括以下信息： 学生信息：学号、姓名、性别、年级、密码 课程信息：课程编号、课程名称、已选人数、可选人数、授课教师。2.基本功能需求： （1）使用命令行完成系统的功能设计； （2）启动程序，输出"学生选课管理——登录"。（2）提示客户输入学号、密码。3.其他功能需求： （1） 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; （2）文件StudentDB.java：单列类，模拟数据库中的课程，初始化后至少封装5名学生信息; （3）文件登录.java：负责登录的业务逻辑; （4）文件SelectCourse.java：负责选课的业务逻辑; （5）文件MainProcess.java：负责整体业务流程; （6）学生选课成功后，选课状态变更为“已选”，否则，课程状态变更为“可选”;学生选择“已选”课程，提示“该课程无法重复选择”;（7）学生选课成功后，选课人数相应发生变化；代码

以下是Java学生选课系统的代码实现，包含了上述基本功能需求和其他功能需求：

Course.java：

public class Course {
    private String courseId;
    private String courseName;
    private int selectedNum;
    private int availableNum;
    private String teacher;

    public Course(String courseId, String courseName, int selectedNum, int availableNum, String teacher) {
        this.courseId = courseId;
        this.courseName = courseName;
        this.selectedNum = selectedNum;
        this.availableNum = availableNum;
        this.teacher = teacher;
    }

    public String getCourseId() {
        return courseId;
    }

    public String getCourseName() {
        return courseName;
    }

    public int getSelectedNum() {
        return selectedNum;
    }

    public int getAvailableNum() {
        return availableNum;
    }

    public String getTeacher() {
        return teacher;
    }

    public void setSelectedNum(int selectedNum) {
        this.selectedNum = selectedNum;
    }

    public void setAvailableNum(int availableNum) {
        this.availableNum = availableNum;
    }
}

CourseDB.java：

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

public class CourseDB {
    private static CourseDB instance = new CourseDB();

    private List<Course> courseList;

    private CourseDB() {
        courseList = new ArrayList<>();
        courseList.add(new Course("001", "Java入门", 0, 2, "张三"));
        courseList.add(new Course("002", "Java进阶", 0, 1, "李四"));
        courseList.add(new Course("003", "Java高级", 0, 3, "王五"));
        courseList.add(new Course("004", "Python入门", 0, 2, "赵六"));
        courseList.add(new Course("005", "Python进阶", 0, 1, "钱七"));
        courseList.add(new Course("006", "Python高级", 0, 3, "孙八"));
        courseList.add(new Course("007", "C++入门", 0, 2, "周九"));
        courseList.add(new Course("008", "C++进阶", 0, 1, "吴十"));
        courseList.add(new Course("009", "C++高级", 0, 3, "郑一"));
        courseList.add(new Course("010", "数据结构", 0, 2, "孔二"));
    }

    public static CourseDB getInstance() {
        return instance;
    }

    public List<Course> getCourseList() {
        return courseList;
    }

    public Course getCourseById(String courseId) {
        for (Course course : courseList) {
            if (course.getCourseId().equals(courseId)) {
                return course;
            }
        }
        return null;
    }
}

Student.java：

public class Student {
    private String studentId;
    private String name;
    private String gender;
    private String grade;
    private String password;

    public Student(String studentId, String name, String gender, String grade, String password) {
        this.studentId = studentId;
        this.name = name;
        this.gender = gender;
        this.grade = grade;
        this.password = password;
    }

    public String getStudentId() {
        return studentId;
    }

    public String getName() {
        return name;
    }

    public String getGender() {
        return gender;
    }

    public String getGrade() {
        return grade;
    }

    public String getPassword() {
        return password;
    }
}

StudentDB.java：

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

public class StudentDB {
    private static StudentDB instance = new StudentDB();

    private List<Student> studentList;

    private StudentDB() {
        studentList = new ArrayList<>();
        studentList.add(new Student("1001", "张三", "男", "大一", "123456"));
        studentList.add(new Student("1002", "李四", "女", "大二", "123456"));
        studentList.add(new Student("1003", "王五", "男", "大三", "123456"));
        studentList.add(new Student("1004", "赵六", "女", "大四", "123456"));
        studentList.add(new Student("1005", "钱七", "男", "大一", "123456"));
    }

    public static StudentDB getInstance() {
        return instance;
    }

    public List<Student> getStudentList() {
        return studentList;
    }

    public Student getStudentById(String studentId) {
        for (Student student : studentList) {
            if (student.getStudentId().equals(studentId)) {
                return student;
            }
        }
        return null;
    }
}

Login.java：

import java.util.Scanner;

public class Login {
    public static Student login() {
        Scanner input = new Scanner(System.in);

        System.out.println("学生选课管理——登录");
        System.out.print("请输入学号：");
        String studentId = input.nextLine();
        System.out.print("请输入密码：");
        String password = input.nextLine();

        Student student = StudentDB.getInstance().getStudentById(studentId);

        if (student == null) {
            System.out.println("该学号不存在，请重新输入。");
            return null;
        }

        if (!student.getPassword().equals(password)) {
            System.out.println("密码错误，请重新输入。");
            return null;
        }

        return student;
    }
}

SelectCourse.java：

import java.util.List;
import java.util.Scanner;

public class SelectCourse {
    public static void select(Student student) {
        Scanner input = new Scanner(System.in);

        while (true) {
            System.out.println("请输入要选的课程编号（输入0退出）：");
            List<Course> courseList = CourseDB.getInstance().getCourseList();
            for (Course course : courseList) {
                System.out.printf("%s\t%s\t%d/%d\t%s\n", course.getCourseId(), course.getCourseName(),
                        course.getSelectedNum(), course.getAvailableNum(), course.getTeacher());
            }

            String courseId = input.nextLine();
            if (courseId.equals("0")) {
                break;
            }

            Course course = CourseDB.getInstance().getCourseById(courseId);
            if (course == null) {
                System.out.println("该课程不存在，请重新输入。");
                continue;
            }

            if (course.getSelectedNum() >= course.getAvailableNum()) {
                System.out.println("该课程已满，请选择其他课程。");
                continue;
            }

            if (studentHasSelectedCourse(student, courseId)) {
                System.out.println("您已经选过该课程，请选择其他课程。");
                continue;
            }

            course.setSelectedNum(course.getSelectedNum() + 1);
            studentSelectCourse(student, course);
            System.out.println("选课成功！");
        }
    }

    private static boolean studentHasSelectedCourse(Student student, String courseId) {
        List<Course> selectedCourseList = student.getSelectedCourseList();
        for (Course course : selectedCourseList) {
            if (course.getCourseId().equals(courseId)) {
                return true;
            }
        }
        return false;
    }

    private static void studentSelectCourse(Student student, Course course) {
        List<Course> selectedCourseList = student.getSelectedCourseList();
        selectedCourseList.add(course);
        student.setSelectedCourseList(selectedCourseList);
        course.setSelectedNum(course.getSelectedNum() + 1);
        course.setAvailableNum(course.getAvailableNum() - 1);
    }
}

MainProcess.java：

public class MainProcess {
    public static void main(String[] args) {
        Student student = null;
        while (student == null) {
            student = Login.login();
        }

        SelectCourse.select(student);
    }
}

注意，以上代码只是一个基本的实现，实际情况可能需要更多的逻辑判断和错误处理。