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。

教材类：

public class Textbook {
    private String name;
    private String author;
    private String publisher;
    private int year;

    public Textbook(String name, String author, String publisher, int year) {
        this.name = name;
        this.author = author;
        this.publisher = publisher;
        this.year = year;
    }

    // getter and setter methods

    public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

}

课程类：

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

public class Course {
    private String name;
    private List<Textbook> textbooks;

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

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

    // getter and setter methods

    public String getName() {
        return name;
    }

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

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

    public void setTextbooks(List<Textbook> textbooks) {
        this.textbooks = textbooks;
    }
}

为某门课程指定参考教材的类：

public class CourseTextbook {
    private Course course;
    private Textbook textbook;

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

    // getter and setter methods

    public Course getCourse() {
        return course;
    }

    public void setCourse(Course course) {
        this.course = course;
    }

    public Textbook getTextbook() {
        return textbook;
    }

    public void setTextbook(Textbook textbook) {
        this.textbook = textbook;
    }
}

测试类：

public class Test {
    public static void main(String[] args) {
        // create textbooks
        Textbook textbook1 = new Textbook("Java Programming", "John Smith", "ABC Publisher", 2020);
        Textbook textbook2 = new Textbook("Python Programming", "Emily Lee", "XYZ Publisher", 2019);

        // create courses
        Course course1 = new Course("Java Programming");
        Course course2 = new Course("Python Programming");

        // assign textbooks to courses
        CourseTextbook ct1 = new CourseTextbook(course1, textbook1);
        CourseTextbook ct2 = new CourseTextbook(course2, textbook2);

        // print out course information and its textbooks
        System.out.println("Course: " + course1.getName());
        for (Textbook t : course1.getTextbooks()) {
            System.out.println("Textbook: " + t.getName() + " by " + t.getAuthor());
        }

        System.out.println("Course: " + course2.getName());
        for (Textbook t : course2.getTextbooks()) {
            System.out.println("Textbook: " + t.getName() + " by " + t.getAuthor());
        }
    }
}