class Emp{    private int empno;//职工编号    private String ename;//姓名    private String job;//职位    private double sal;//基本工资    private double comm;    private Emp mgr;//所属领导    private  Dept dept;//所在部门    public Emp(){}//无参构造    public Emp(int empno,String ename,String job,double sal,double comm){
   //有参构造        this.empno = empno;        this.ename = ename;        this.job = job;        this.sal = sal;        this.comm = comm;    }    public void setMgr(Emp mgr) {
   //传递领导信息        this.mgr = mgr;    }    public Emp getMgr(){
   //获取领导信息        return this.mgr;    }    public void setDept(Dept dept) {
   //设置部门信息        this.dept = dept;    }    public Dept getDept() {
   //读取部门信息        return dept;    }    public String getInfo(){        return "职工编号："+this.empno +"，职工姓名：" + this.ename + "，职工职位：" + this.job + "，基本工资：" + this.sal                +"，提成：" + this.comm;    }}class Dept{    private int deptno;    private String dname;//部门名称    private String loc;//部门地址    private Emp[] emps;//所有员工    public Dept(){ }    public Dept(int deptno,String dname,String loc){        this.deptno = deptno;        this.dname = dname;        this.loc = loc;    }    public void setEmps(Emp[] emps) {        this.emps = emps;    }    public Emp[] getEmps() {        return emps;    }    public String getInfo(){        return "部门编号：" + this.deptno +"，部门名称：" + this.dname +",所在地址：" + this.loc;    }}public class Main {    public static void main(String[] args) {        // 创建各自的实例化对象        Dept dept = new Dept(10,"ACCOUNTING","NEW YORK");        Emp ea = new Emp(7369,"SMITH","CLERK",800.0,0.0);        Emp eb = new Emp(7466,"ALLEN","MANAGER",2450.0,0.0);        Emp ec = new Emp(7839,"KING","PRESIDENT",5000.0,0.0);        //设置领导关系        ea.setMgr(eb);        eb.setMgr(ec);//ec对象没有领导，因为他是头        //设置员工和部门关系        ea.setDept(dept);        eb.setDept(dept);        ec.setDept(dept);        //设置部门和员工的关系        dept.setEmps(new Emp[]{ea,eb,ec});        //读取数据        System.out.println(dept.getInfo());//输出部门信息        for(int x=0;x

上面代码是实现一对多的数据表，基于公司人事管理的例子（根据员工可以输出其基本信息及所在部门信息和所属领导信息，根据部门可以输出所有员工及领导），在Java一对多的数据关系中，需要遵循以下设计原则：

简单Java类设计原则：Java类与数据表的关系

　　1、Java的名称 = 实体表的名称

　　2、Java类的属性 = 实体表的字段

　　3、Java类的一个对象 = 表的一行记录

　　4、对象数组 = 表的多行记录

　　5、外键关系 = 引用配置

 

多对多的数据表（学生成绩管理）：根据学生可以输出所修课程信息及成绩，根据课程可以输出学习该课程的学生信息及成绩

class Student{
   //学生表    private int stuid;    private String sname;    private int age;    private StudentCourse studentCourse[];//学生成绩信息    public Student(){}    public Student(int stuid,String sname,int age){        this.stuid = stuid;        this.sname = sname;        this.age = age;    }    public void setStudentCourse(StudentCourse[] studentCourse) {        this.studentCourse = studentCourse;    }    public StudentCourse[] getStudentCourse() {        return studentCourse;    }    public String getInfo(){        return "学号：" + this.stuid + "，学生姓名：" + this.sname + "，年龄：" + this.age;    }}class Course{//课程表    private String name;    private int cid;    private int credit;    private StudentCourse studentCourse[];    public Course(){}    public Course(String name,int cid,int credit){        this.cid = cid;        this.name = name;        this.credit = credit;    }    public StudentCourse[] getStudentCourse() {        return studentCourse;    }    public void setStudentCourse(StudentCourse[] studentCourse) {        this.studentCourse = studentCourse;    }    public String getInfo(){        return "课号：" + this.credit + "，名称：" + this.name + ",学分：" + this.credit;    }}class StudentCourse{
   //学生选课表    private Student student;    private Course course;    private double score;//成绩    public StudentCourse(){    }    public StudentCourse(Student student,Course course,double score){        this.course = course;        this.score = score;        this.student = student;    }    public Course getCourse() {        return course;    }    public Student getStudent() {        return student;    }    public double getScore() {        return score;    }}public class Main {    public static void main(String[] args) {        //创建各自的独立对象        Student stu1 = new Student(1,"张三",18);        Student stu2 = new Student(1,"李四",20);        Student stu3 = new Student(1,"王五",19);        Course ca = new Course("高等数学",1001,5);        Course cb = new Course("线性代数",1002,4);        //设置各自的关系        //设置学生和课程的关系        stu1.setStudentCourse(new StudentCourse[]{                new StudentCourse(stu1,ca,92.5),                new StudentCourse(stu1,cb,94.0)        });        stu2.setStudentCourse(new StudentCourse[]{                new StudentCourse(stu2,ca,89.0)        });        stu3.setStudentCourse(new StudentCourse[]{                new StudentCourse(stu3,cb,95.0),                new StudentCourse(stu3,ca,90.5)        });        //设置课程和学生的关系        ca.setStudentCourse(new StudentCourse[]{                new StudentCourse(stu1,ca,92.5),                new StudentCourse(stu2,ca,89.0)                new StudentCourse(stu3,ca,90.5)        });        cb.setStudentCourse(new StudentCourse[]{                new StudentCourse(stu1,cb,94.0),                new StudentCourse(stu3,cb,95.0)        });        //找到一门课程，并且输出学习此课程的所有学生的信息及成绩        System.out.println(ca.getInfo());        for(int x = 0;x < ca.getStudentCourse().length;x++){            System.out.println("\t"+ca.getStudentCourse()[x].getStudent().getInfo()                    +",成绩："+ca.getStudentCourse()[x].getScore());        };        System.out.println("***********");        //根据学生输出其信息及选修的课程信息和所得成绩        System.out.println(stu1.getInfo());        for(int x = 0;x < stu1.getStudentCourse().length;x++){            System.out.println("\t选修课程：" + stu1.getStudentCourse()[x].getCourse().getInfo()                    + "，所得成绩：" + stu1.getStudentCourse()[x].getScore());        }    }}