在IDEA中用JAVA设计一个教材类，一个课程类，及一个为某门课程指定参考教材的类。一门课程可以有多本参考教材，再设计一个测试类。 设计一个简单的学生选课系统，并可以完成添加、删除、修改、查询相关信息 。 说明： 可以设计以下类： 描述课程基本信息类(课程编号，课程名，学分 )； 描述学生基本信息类(学号，姓名，专业方向 )； 记录选课结果的类(课程，选课的学生，课程最多人数，当前人数 )； 测试类(设定或输入最多人数，创建课程对象，创建选课学生对象，创建选课对象，显示选课情况 )

好的，我可以帮您解答这个问题。下面是代码实现：

教材类：

public class Textbook {
    private String name; // 教材名称
    private String author; // 作者
    private double price; // 价格

    public Textbook(String name, String author, double price) {
        this.name = name;
        this.author = author;
        this.price = price;
    }

    public String getName() {
        return name;
    }

    public String getAuthor() {
        return author;
    }

    public double getPrice() {
        return price;
    }
}

课程类：

import java.util.ArrayList;

public class Course {
    private String id; // 课程编号
    private String name; // 课程名称
    private int credit; // 学分
    private ArrayList<Textbook> textbooks; // 参考教材

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

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getCredit() {
        return credit;
    }

    public void addTextbook(Textbook textbook) {
        textbooks.add(textbook);
    }

    public ArrayList<Textbook> getTextbooks() {
        return textbooks;
    }
}

为某门课程指定参考教材的类：

public class CourseTextbook {
    private Course course; // 课程
    private Textbook textbook; // 参考教材

    public CourseTextbook(Course course, Textbook textbook) {
        this.course = course;
        this.textbook = textbook;
        course.addTextbook(textbook);
    }

    public Course getCourse() {
        return course;
    }

    public Textbook getTextbook() {
        return textbook;
    }
}

学生基本信息类：

public class Student {
    private String id; // 学号
    private String name; // 姓名
    private String major; // 专业方向

    public Student(String id, String name, String major) {
        this.id = id;
        this.name = name;
        this.major = major;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getMajor() {
        return major;
    }
}

记录选课结果的类：

import java.util.ArrayList;

public class CourseSelection {
    private Course course; // 课程
    private int maxNum; // 课程最多人数
    private ArrayList<Student> students; // 选课的学生

    public CourseSelection(Course course, int maxNum) {
        this.course = course;
        this.maxNum = maxNum;
        students = new ArrayList<>();
    }

    public boolean addStudent(Student student) {
        if (students.size() >= maxNum) {
            return false;
        }
        students.add(student);
        return true;
    }

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

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

测试类：

public class Test {
    public static void main(String[] args) {
        // 设定或输入最多人数
        int maxNum = 50;

        // 创建课程对象
        Course math = new Course("001", "高等数学", 3);
        Course physics = new Course("002", "大学物理", 4);

        // 创建参考教材对象
        Textbook mathTextbook1 = new Textbook("高等数学（第一册）", "李永乐", 50);
        Textbook mathTextbook2 = new Textbook("高等数学（第二册）", "李永乐", 60);
        Textbook physicsTextbook1 = new Textbook("大学物理（第一册）", "张伯礼", 80);

        // 为课程指定参考教材
        CourseTextbook mathTextbook = new CourseTextbook(math, mathTextbook1);
        CourseTextbook mathTextbook2 = new CourseTextbook(math, mathTextbook2);
        CourseTextbook physicsTextbook = new CourseTextbook(physics, physicsTextbook1);

        // 创建选课学生对象
        Student student1 = new Student("1001", "张三", "计算机科学");
        Student student2 = new Student("1002", "李四", "计算机科学");
        Student student3 = new Student("1003", "王五", "软件工程");

        // 创建选课对象
        CourseSelection mathSelection = new CourseSelection(math, maxNum);
        CourseSelection physicsSelection = new CourseSelection(physics, maxNum);

        // 添加选课学生
        mathSelection.addStudent(student1);
        mathSelection.addStudent(student2);
        mathSelection.addStudent(student3);
        physicsSelection.addStudent(student1);
        physicsSelection.addStudent(student2);

        // 显示选课情况
        System.out.println(math.getName() + "选课情况：");
        System.out.println("课程编号：" + math.getId());
        System.out.println("学分：" + math.getCredit());
        System.out.println("参考教材：");
        ArrayList<Textbook> mathTextbooks = math.getTextbooks();
        for (Textbook textbook : mathTextbooks) {
            System.out.println(textbook.getName() + " " + textbook.getAuthor() + " " + textbook.getPrice());
        }
        System.out.println("选课人数：" + mathSelection.getStudents().size());
        System.out.println("选课学生：");
        ArrayList<Student> mathStudents = mathSelection.getStudents();
        for (Student student : mathStudents) {
            System.out.println(student.getId() + " " + student.getName() + " " + student.getMajor());
        }
        System.out.println();

        System.out.println(physics.getName() + "选课情况：");
        System.out.println("课程编号：" + physics.getId());
        System.out.println("学分：" + physics.getCredit());
        System.out.println("参考教材：");
        ArrayList<Textbook> physicsTextbooks = physics.getTextbooks();
        for (Textbook textbook : physicsTextbooks) {
            System.out.println(textbook.getName() + " " + textbook.getAuthor() + " " + textbook.getPrice());
        }
        System.out.println("选课人数：" + physicsSelection.getStudents().size());
        System.out.println("选课学生：");
        ArrayList<Student> physicsStudents = physicsSelection.getStudents();
        for (Student student : physicsStudents) {
            System.out.println(student.getId() + " " + student.getName() + " " + student.getMajor());
        }
    }
}

通过上述代码实现，我们就可以简单地设计一个学生选课系统，并可以完成添加、删除、修改、查询相关信息。