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<dept.getEmps().length;x++){
System.out.println("\t"+dept.getEmps()[x].getInfo());
if(dept.getEmps()[x].getMgr()!=null){ //若有领导
System.out.println("\t"+dept.getEmps()[x].getMgr().getInfo());
}
}
System.out.println("************************");
//根据员工找到对应的领导信息和部门信息
System.out.println(eb.getInfo());
if(eb.getMgr()!=null)
System.out.println("\t"+eb.getMgr().getInfo());
if(eb.getDept()!=null)
System.out.println("\t"+eb.getDept().getInfo());
}
}
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());
}
}
}