private List<Course> courses; private CourseDB() { courses = new ArrayList<>(); courses.add(new Course("C001", "Java Programming", 50, "Mr. Zhang")); courses.add(new Course("C002", "Web Development", 40, "Ms. Li")); courses.add(new Course("C003", "Database Design", 30, "Mr. Wang")); courses.add(new Course("C004", "Data Structures", 60, "Ms. Zhao")); courses.add(new Course("C005", "Artificial Intelligence", 20, "Mr. Liu")); courses.add(new Course("C006", "Computer Networks", 35, "Ms. Chen")); courses.add(new Course("C007", "Operating Systems", 25, "Mr. Wu")); courses.add(new Course("C008", "Cybersecurity", 30, "Ms. Huang")); courses.add(new Course("C009", "Software Engineering", 45, "Mr. Xu")); courses.add(new Course("C010", "Mobile App Development", 20, "Ms. Zhang")); } public static CourseDB getInstance() { if (instance == null) { instance = new CourseDB(); } return instance; } public List<Course> getAllCourses() { return courses; } public Course getCourseById(String id) { for (Course course : courses) { if (course.getId().equals(id)) { return course; }

这段代码是一个CourseDB类，其中包含一个私有的List<Course>类型的变courses，用于存储课程信息。在CourseDB类的构造方法中，初始化了courses列表，添加了10门课程的信息。CourseDB类使用了单例模式，getInstance()方法可以获取CourseDB类的实例。getAllCourses()方法返回所有课程的信息列表courses，getCourseById()方法根据课程id获取对应的课程信息。

这段代码没有明显的报错，但是如果你在使用时出现了问题，可以提供更具体的错误信息和使用代码，我可以帮你更好地分析和解决问题。

相关问题

利用java程序定义文件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

好的，下面是一个示例的 CourseDB 类，它是一个单例类，用于模拟数据库中的课程，初始化后至少封装了10门课程：

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

public class CourseDB {
    private static CourseDB instance = null; // 单例实例
    private List<Course> courses; // 课程列表

    private CourseDB() {
        // 初始化至少10门课程
        courses = new ArrayList<>();
        courses.add(new Course("C001", "Java Programming", 50, "John Smith"));
        courses.add(new Course("C002", "Data Structures and Algorithms", 60, "Mary Johnson"));
        courses.add(new Course("C003", "Database Management", 40, "Tom Lee"));
        courses.add(new Course("C004", "Web Development", 45, "Lucy Chen"));
        courses.add(new Course("C005", "Operating Systems", 55, "David Wang"));
        courses.add(new Course("C006", "Artificial Intelligence", 30, "Emily Liu"));
        courses.add(new Course("C007", "Computer Networks", 50, "James Chen"));
        courses.add(new Course("C008", "Software Engineering", 40, "Grace Zhang"));
        courses.add(new Course("C009", "Machine Learning", 35, "Richard Wu"));
        courses.add(new Course("C010", "Human-Computer Interaction", 30, "Michelle Li"));
    }

    // 获取单例实例
    public static CourseDB getInstance() {
        if (instance == null) {
            instance = new CourseDB();
        }
        return instance;
    }

    // 获取所有课程列表
    public List<Course> getCourses() {
        return courses;
    }

    // 根据课程编号获取课程信息
    public Course getCourse(String code) {
        for (Course course : courses) {
            if (course.getCode().equals(code)) {
                return course;
            }
        }
        return null;
    }
}

在这个示例中，我们使用单例模式来实现 CourseDB 类，在构造函数中初始化至少10门课程。我们提供了一个公有的静态方法 getInstance() 来获取单例实例。我们还提供了两个公有方法，getCourses() 方法返回所有课程的列表，getCourse(String code) 方法根据课程编号返回指定的课程信息。课程信息是一个 Course 类的对象，其中包含了课程编号、课程名称、可选人数和授课教师等属性。

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。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；文件Login.java:负责登录的业务逻辑；文件SelectCourse.java：负责选课的业务逻辑；文件MainProcess.java：负责整体业务流程；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”；学生选课成功后，选课人数相应发生变化

好的，以下是一个基本的Java实现学生选课系统的代码：

CourseDB.java

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

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

    private CourseDB() {
        courses = new ArrayList<>();
        courses.add(new Course("C001", "Java Programming", 0, 10, "Tom"));
        courses.add(new Course("C002", "Data Structure", 0, 15, "John"));
        courses.add(new Course("C003", "Algorithm Analysis", 0, 20, "Lucy"));
        courses.add(new Course("C004", "Database Management", 0, 15, "Bob"));
        courses.add(new Course("C005", "Web Development", 0, 12, "Alice"));
        courses.add(new Course("C006", "Mobile Application Development", 0, 8, "Jack"));
        courses.add(new Course("C007", "Artificial Intelligence", 0, 20, "David"));
        courses.add(new Course("C008", "Computer Networks", 0, 18, "Sarah"));
        courses.add(new Course("C009", "Operating System", 0, 15, "Mike"));
        courses.add(new Course("C010", "Computer Graphics", 0, 10, "Lisa"));
    }

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

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

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }
}

StudentDB.java

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

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

    private StudentDB() {
        students = new ArrayList<>();
        students.add(new Student("S001", "张三", "男", "大一", "123456"));
        students.add(new Student("S002", "李四", "女", "大二", "123456"));
        students.add(new Student("S003", "王五", "男", "大三", "123456"));
        students.add(new Student("S004", "赵六", "女", "大四", "123456"));
        students.add(new Student("S005", "陈七", "男", "大一", "123456"));
    }

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

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

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}

Login.java

import java.util.Scanner;

public class Login {
    public static Student login() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入学号：");
        String id = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();

        StudentDB studentDB = StudentDB.getInstance();
        for (Student student : studentDB.getStudents()) {
            if (student.getId().equals(id) && student.getPassword().equals(password)) {
                return student;
            }
        }
        return null;
    }
}

SelectCourse.java

import java.util.Scanner;

public class SelectCourse {
    public static void selectCourse(Student student) {
        CourseDB courseDB = CourseDB.getInstance();
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("请选择课程（输入课程编号，输入0退出）：");
            for (Course course : courseDB.getCourses()) {
                System.out.println(course.getCourseId() + " " + course.getCourseName() + " " +
                        course.getTeacher() + " " + course.getSelectedNum() + "/" + course.getTotalNum());
            }
            String courseId = scanner.nextLine();
            if (courseId.equals("0")) {
                break;
            }
            Course selectedCourse = null;
            for (Course course : courseDB.getCourses()) {
                if (course.getCourseId().equals(courseId)) {
                    selectedCourse = course;
                    break;
                }
            }
            if (selectedCourse == null) {
                System.out.println("输入的课程编号不存在，请重新输入！");
                continue;
            }
            if (selectedCourse.getSelectedNum() >= selectedCourse.getTotalNum()) {
                System.out.println("该课程已选满，请重新选择！");
                continue;
            }
            if (student.getSelectedCourses().contains(selectedCourse)) {
                System.out.println("该课程已选过，请重新选择！");
                continue;
            }
            selectedCourse.setSelectedNum(selectedCourse.getSelectedNum() + 1);
            student.getSelectedCourses().add(selectedCourse);
            System.out.println("选课成功！");
        }
    }
}

MainProcess.java

public class MainProcess {
    public static void main(String[] args) {
        Student student = Login.login();
        if (student != null) {
            System.out.println("欢迎" + student.getName() + "登录选课系统！");
            SelectCourse.selectCourse(student);
        } else {
            System.out.println("学号或密码错误，登录失败！");
        }
    }
}

Course.java

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

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

    public String getCourseId() {
        return courseId;
    }

    public void setCourseId(String courseId) {
        this.courseId = courseId;
    }

    public String getCourseName() {
        return courseName;
    }

    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }

    public int getSelectedNum() {
        return selectedNum;
    }

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

    public int getTotalNum() {
        return totalNum;
    }

    public void setTotalNum(int totalNum) {
        this.totalNum = totalNum;
    }

    public String getTeacher() {
        return teacher;
    }

    public void setTeacher(String teacher) {
        this.teacher = teacher;
    }
}

Student.java

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

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

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

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getGrade() {
        return grade;
    }

    public void setGrade(String grade) {
        this.grade = grade;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public List<Course> getSelectedCourses() {
        return selectedCourses;
    }

    public void setSelectedCourses(List<Course> selectedCourses) {
        this.selectedCourses = selectedCourses;
    }
}