Java多对多映射

多对对的映射，可以用学生和课程进行演示。一个学生可以选择多个课程，一个课程又对应了多个学生

定义学生类

class Stu{
    private String name;
    private String num;
    private Course[] course;
    public Stu() {}
    public Stu(String name,String num) {
        this.name = name;
        this.num = num;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getNum() {
        return num;
    }
    public void setNum(String num) {
        this.num = num;
    }
    public Course[] getCourse() {
        return course;
    }
    public void setCourse(Course[] course) {
        this.course = course;
    }
    public String getInfo() {
        return "姓名 :"+name+" 学号 :"+num;
    }
}

定义课程 类

class Course{
    private String name;
    private Stu[] stu;
    public Course() {}
    public Course(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Stu[] getStu() {
        return stu;
    }
    public void setStu(Stu[] stu) {
        this.stu = stu;
    }
    public String getInfo() {
        return "课程  :"+name;
    }
    
    
}

在main方法测试

首先定义Stu和Course对象，分别有三个

        Stu s1 = new Stu("张三","001");
        Stu s2 = new Stu("李四","002");
        Stu s3 = new Stu("王五","003");
        
        Course c1 = new Course("Java");
        Course c2 = new Course("php");
        Course c3 = new Course("Python");

设置彼此的关系，每个对象都有多个对象对应

        //设置学生和课程的关系
        s1.setCourse(new Course[]{c1,c2});
        s2.setCourse(new Course[]{c1,c3});
        s3.setCourse(new Course[]{c2,c3});
        
        //相应的课程设置与学生的关系
        c1.setStu(new Stu[]{s1,s2});
        c2.setStu(new Stu[]{s1,s3});
        c3.setStu(new Stu[]{s2,s3});

根据学生，获取课程信息

        System.out.println(s1.getInfo()+" 同学选择的课程有");
        for(int i=0; i<s1.getCourse().length; i++) {
            System.out.println(s1.getCourse()[i].getInfo());
        }

运行

根据课程，获取学生信息

        System.out.println(c2.getInfo()+" 选择这门课程的学生信息");
        for(int i=0; i<c2.getStu().length; i++) {
            System.out.println(c2.getStu()[i].getInfo());
        }

运行