Map实现一个键对应多个值

//班级类
public class Clazz {
    private int classNum;                        //班级号
    private ArrayList list = new ArrayList();    //每个班配一个集合来放学生
    //构造器
    public Clazz(int n){
        super();
        classNum = n;
    }
    //添加学生
    public void addStudent(Student s){
        list.add(s);
    }
    
    //得到学生序列
    public ArrayList getStudentList(){
        return list;
    }
    
    //班上学生总分
    public int getSumScores(){
        int sum = 0;
        for (Object object : list) {
            Student s = (Student)object;
            sum+=s.getScore();
        }
        return sum;
    }
    
    //班上学生平均分
    public double getAverageScore(){
        double average = 0;
        average = getSumScores()*1.0/list.size();
        return average;
    }
    //打印班级成绩信息
    public void printClassScore(int classNumber){
        HashMap map = new HashMap();
        //存入到map中   key为classNumber ， values为班上学生总分
        map.put(classNumber,getSumScores());
        //输出
        System.out.println(classNumber+"班的总分为："+map.get(classNumber)+"  平均分为："+getAverageScore());
    }
}

public class Test6 {

    public static void main(String[] args) {
        //创建相应班级
        Clazz c1 = new Clazz(1);
        Clazz c2 = new Clazz(2);
        //创建学生
        Student s1 = new Student("一班一号", 1, 60);    //姓名 班级 个人成绩
        Student s2 = new Student("一班二号", 1, 70);
        Student s3 = new Student("一班三号", 1, 80);
        Student s4 = new Student("二班四号", 2, 80);
        Student s5 = new Student("二班五号", 2, 80);
        Student s6 = new Student("二班六号", 2, 80);
        
        //添加学生到相应班级
        c1.addStudent(s1);
        c1.addStudent(s2);
        c1.addStudent(s3);
        
        c2.addStudent(s4);
        c2.addStudent(s5);
        c2.addStudent(s6);
        
        //输出
        c1.printClassScore(1);
        c2.printClassScore(2);
    }

}