请问老师，平均分排序问题该怎么做？

package studentmanagement;

import java.util.Objects;

public class Student {
    private String stuNum;//学号
    private String stuName;//名字
    private float math;//数学分数
    private float chinese;//语文分数

    public Student(String stuNum, String stuName, float math, float chinese) {
        this.stuNum = stuNum;
        this.stuName = stuName;
        this.math = math;
        this.chinese = chinese;
    }

    /**
     * 判断学生是否存在
     * @param o 学生
     * @return  是否存在
     */
    @Override
    public boolean equals(Object o) {
    if(this==o){
        return true;
    }else{
        if(o.getClass()==Student.class){
            Student sd=(Student) o;
            return (sd.getStuNum().equals(stuNum))&&
                    (sd.getStuName().equals(stuName));
        }
    }
    return false;
    }

    @Override
    public String toString() {
        return "{" +
                "学生编号='" + stuNum + '\'' +
                ", 学生名字='" + stuName + '\'' +
                ", 数学成绩=" + math +
                ", 语文成绩=" + chinese +
                '}';
    }

    @Override
    public int hashCode() {
        return Objects.hash(stuNum, stuName, math, chinese);
    }

    public String getStuNum() {
        return stuNum;
    }

    public void setStuNum(String stuNum) {
        this.stuNum = stuNum;
    }

    public String getStuName() {
        return stuName;
    }

    public void setStuName(String stuName) {
        this.stuName = stuName;
    }

    public float getMath() {
        return math;
    }

    public void setMath(float math) {
        this.math = math;
    }

    public float getChinese() {
        return chinese;
    }

    public void setChinese(float chinese) {
        this.chinese = chinese;
    }
}

package studentmanagement;

import com.imooc.Player.PlayList;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class School {
    private Map<String,BanJi> schoolMap;//存放班级的集合


    public School() {
        schoolMap=new HashMap<String,BanJi>();

    }

    /**
     * 添加班级
     * @param banji
     */
    public void addBanji(BanJi banji){
        //添加班级，键对值：班级id，班级
        schoolMap.put(banji.getClassName(),banji);
    }

    /**
     * 删除班级
     * @param banji
     */
    public void deleteBanji(BanJi banji){
        System.out.println("您要删除的是："+banji.getClassId()+"   "+banji.getClassName());
        schoolMap.remove(banji.getClassName());
        System.out.println("删除成功！");
    }

    /**
     * 通过班级名称查询班级
     * @param className 班级名称
     */
    public BanJi searchByName(String className) {
        BanJi banji=null;
        Set<String> banjiSet=schoolMap.keySet();
        for(String s:banjiSet){
            if(s.equals(className)){
                //如果查到了，储存到banji上
                banji=schoolMap.get(s);
                System.out.println("班级的id为："+banji.getClassId()+"    班级的名字为："+banji.getClassName());
                break;
            }
        }
        return banji;
//    }
    }

    /**
     *对各班语文成绩按平均分进行由大到小排序
     */
    public void sortChineseByAverage() {

    }

    /**
     *对各班数学成绩按平均分进行由大到小排序
     */
    public void sortMathByAverage() {}

    /**
     * 显示所有班级名称
     */
    public void displayBanJiName() {
        Set<String> schoolMapSet=schoolMap.keySet();
        System.out.println("现有班级为：：");
        for(String s:schoolMapSet){
            System.out.println(s);
        }
    }

}

package studentmanagement;

import com.imooc.Player.Song;

import java.util.ArrayList;
import java.util.List;

public class BanJi {
    private String classId;//班级编号
    private String className;//班级名字
    private List<Student> stuList;//存放学生的集合

    public BanJi(String classId, String className) {
        this.classId = classId;
        this.className = className;

        stuList=new ArrayList<Student>();
    }

    public String getClassId() {
        return classId;
    }

    public void setClassId(String classId) {
        this.classId = classId;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className = className;
    }

    public List getStuList() {
        return stuList;
    }

    public void setStuList(List stuList) {
        this.stuList = stuList;
    }

    /**
     * 将学生添加进班级
     * @param stu 学生
     */
    public void addStudent(Student stu){
        //判断是否存在
        Boolean flag=false;
        for(Student stu1:stuList){
            if(stu1.equals(stu)){
                flag=true;
                //System.out.println("添加失败，该学生已经存在!!");
                break;
            }

        }
        if(flag){
            System.out.println("添加失败，该学生已经存在!!");
        }else{
            stuList.add(stu);
            System.out.println("添加成功！");
        }



    }

    /**
     * 通过学号查询学生在班级中是否存在
     * @param stuNum 学号
     * @return  是否存在
     */
    public Student searchStudentByNum(String stuNum){
    Student sd=null;

        for(Student sd1:stuList){
             if(sd1.getStuNum()==stuNum){
                 //如果相等就找到了
                 sd=sd1;
                 break;
             }
        }
        return sd   ;
    }

    /**
     * 输入班级学生的语文成绩
     * @param stuNum 学生
     * @param score 语文成绩
     */
    public void insertChineseScore(String stuNum,float score){


        Student student1=searchStudentByNum(stuNum);
        if(student1!=null) {
        student1.setChinese(score);
            System.out.println("添加成功");
        }else{
            System.out.println("该学生不存在，请先添加");
        }


    }

    /**
     * 输入班级学生的数学成绩
     * @param stuNum    学生
     * @param score     数学成绩
     */
    public void insertMathScore(String stuNum,float score){
        Student student1=searchStudentByNum(stuNum);
        if(student1!=null) {
            student1.setMath(score);
            System.out.println("添加成功");
        }else{
            System.out.println("该学生不存在，请先添加");
        }
    }

    /**
     * 删除学生信息
     * @param stuNum 学生
     */
    public void deleteStudent(String stuNum){
        Student student2=searchStudentByNum(stuNum);

        if(student2!=null) {
            stuList.remove(student2);
            System.out.println("删除成功");
        }else{
            System.out.println("该学生不存在");
        }


    }

    /**
     * 显示所有学生信息（包括学号和名字)
     */
    public void displayAllStudent(){
        System.out.println("班级中所有学生信息为：");
        for(Student student:stuList){
            System.out.println(student);
        }
    }
}

package studentmanagement;



import java.util.ArrayList;
import java.util.List;

public class TestDemo {




    /**
     * 班级测试
     */
    public void testBanJi(){
        Student student1=new Student("s001","张三",50,60);
        Student student2=new Student("s002","李死",60,70);
        Student student3=new Student("s003","王五",70,80);
        Student student4=new Student("s004","老六",80,90);

        BanJi banji=new BanJi("a001","学前一班");
        banji.addStudent(student1);
        banji.addStudent(student2);
        banji.addStudent(student3);
        banji.addStudent(student4);
        //判断学生是否全部添加到班级里
        banji.displayAllStudent();
        {
            //测试删除方法
            banji.deleteStudent("s002");
            banji.displayAllStudent();
           }
        System.out.println("-----------------------");
        //通过编号查询信息
        System.out.println("查询到的信息为："+banji.searchStudentByNum("s003"));

        System.out.println("-----------------------");
        //添加（修改）语文成绩和数学成绩
        banji.insertChineseScore("s001",99);
        banji.insertMathScore("s001",80);
        System.out.println("查询到的信息为："+banji.searchStudentByNum("s001"));


    }

    /**
     * 学校测试
     */
    public void testSchool(){
        Student student1=new Student("s001","张三",50,60);
        Student student2=new Student("s002","李死",60,70);
        Student student3=new Student("s003","王五",70,80);
        Student student4=new Student("s004","老六",80,90);
        BanJi banji1=new BanJi("a001","一班");
        BanJi banji2=new BanJi("a002","二班");
        BanJi banji3=new BanJi("a003","三班");
        BanJi banji4=new BanJi("a004","四班");

        banji1.addStudent(student1);
        banji1.addStudent(student2);
        banji1.addStudent(student3);
        banji1.addStudent(student4);

        School sh = new School();
        sh.addBanji(banji1);
        sh.addBanji(banji2);
        sh.addBanji(banji3);
        sh.addBanji(banji4);
        //测试查找班级
        BanJi banJi1=sh.searchByName("四班");
        if(banJi1==null){
            System.out.println("班级不存在");
        }
        //删除班级
        sh.deleteBanji(banji2);
        //查看全部班级
        sh.displayBanJiName();



    }
    /**
     * 主菜单
     */

    public void mainMenu(){}
    /**
     * 学校管理菜单
     */
    public void schoolMenu(){}

    /**
     * 班级管理菜单
     */
    public void banJiMenu(){}
    /**
     * 主流程
    */
    public void test(){}

    public static void main(String[] args) {
        TestDemo td=new TestDemo();
//        td.testBanJi();
        td.testSchool();
    }
}

没思路了呀，不会写