学生选课系统：一个学生可以选择多门课程，一门课程也可以被很多学生选择，学生和课程之间是多对多的关系。

首先我们先封装一个学生类，里面有学生的姓名、年龄等属性，还有盛放课程的List集合。然后封装一个课程类，有课程名称，学分还有盛放学生的List集合。最后是一个测试类，在测试类里实例化学生和课程进行测试。

代码如下：

学生类：package com.dr.selectcourse;

import java.util.ArrayList;

import java.util.List;

public class Student {

private String name;

private int age;

private List CourseList;

public Student(String name,int age){

this.setName(name);

this.setAge(age);

this.setCourseList(new ArrayList());

}

public void addCourse(Course course){

this.CourseList.add(course);

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public List getCourseList() {

return CourseList;

}

public void setCourseList(List courseList) {

this.CourseList = courseList;

}

}

课程类：

package com.dr.selectcourse;

import java.util.ArrayList;

import java.util.List;

public class Course {

private String name;

private float score;

private List StudentList;

public Course(String name,float score){

this.setName(name);

this.setScore(score);

this.setStudentList(new ArrayList());

}

public void addStudent(Student student){

this.StudentList.add(student);

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public float getScore() {

return score;

}

public void setScore(float score) {

this.score = score;

}

public List getStudentList() {

return StudentList;

}

public void setStudentList(List studentList) {

this.StudentList = studentList;

}

}

测试类

package com.dr.selectcourse;

import java.util.Iterator;

import java.util.List;

public class SelectCourse {

public static void main(String[] args) {

Course c1=new Course("应用密码学",2.0f);

Course c2=new Course("中小型网络组建",5.0f);

Course c3=new Course("数字水印",2.0f);

Student stu1=new Student("宋可",20);

Student stu2=new Student("田馨",21);

Student stu3=new Student("林岚",21);

Student stu4=new Student("刘昕",22);

Student stu5=new Student("张涵",21);

c1.addStudent(stu1);

stu1.addCourse(c1);

c2.addStudent(stu2);

stu2.addCourse(c2);

c3.addStudent(stu3);

stu3.addCourse(c3);

c1.addStudent(stu4);

stu4.addCourse(c1);

c3.addStudent(stu5);

stu5.addCourse(c3);

System.out.println("学生姓名："+stu1.getName());

Iterator iter1=stu1.getCourseList().iterator();

while(iter1.hasNext()){

Course c=iter1.next();

System.out.println("\t| 课程名称："+c.getName()+"，学分： "+c.getScore());

}

System.out.println("课程名称："+c3.getName());

Iterator iter2=c3.getStudentList().iterator();

while(iter2.hasNext()){

Student s=iter2.next();

System.out.println("\t| 学生姓名："+s.getName()+"，学生年龄："+s.getAge());

}

}

}

运行结果：