补充Student类和StudentManage类，实现学生信息录入、排序、按学号查询学生（如果查询的学生不存在，输出提示信息）， 其中，Student类的成员变量包括：String id ; //学号 String name ; //姓名int grade; //成绩,通过学号删除学生，如果要删除的学生不存在，输出提示信息,修改学生成绩功能，添加一个菜单项 “修改成绩”。请用户输入学号、新成绩，修改指定学生的成绩。如果要修改的学生不存在

好的，下面是代码实现：

Student类：

public class Student implements Comparable<Student> {
    private String id; //学号
    private String name; //姓名
    private int grade; //成绩

    public Student(String id, String name, int grade) {
        this.id = id;
        this.name = name;
        this.grade = grade;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getGrade() {
        return grade;
    }

    public void setGrade(int grade) {
        this.grade = grade;
    }

    @Override
    public int compareTo(Student o) {
        return this.id.compareTo(o.id);
    }

    @Override
    public String toString() {
        return "学号：" + id + "，姓名：" + name + "，成绩：" + grade;
    }
}

StudentManage类：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class StudentManage {
    private ArrayList<Student> studentList;

    public StudentManage() {
        studentList = new ArrayList<>();
    }

    public void addStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入学生学号：");
        String id = scanner.nextLine();
        System.out.println("请输入学生姓名：");
        String name = scanner.nextLine();
        System.out.println("请输入学生成绩：");
        int grade = scanner.nextInt();
        Student student = new Student(id, name, grade);
        studentList.add(student);
        System.out.println("添加成功！");
    }

    public void deleteStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要删除的学生学号：");
        String id = scanner.nextLine();
        boolean flag = false;
        for (int i = 0; i < studentList.size(); i++) {
            Student student = studentList.get(i);
            if (student.getId().equals(id)) {
                studentList.remove(i);
                System.out.println("删除成功！");
                flag = true;
                break;
            }
        }
        if (!flag) {
            System.out.println("要删除的学生不存在！");
        }
    }

    public void modifyGrade() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要修改成绩的学生学号：");
        String id = scanner.nextLine();
        boolean flag = false;
        for (int i = 0; i < studentList.size(); i++) {
            Student student = studentList.get(i);
            if (student.getId().equals(id)) {
                System.out.println("请输入新的成绩：");
                int grade = scanner.nextInt();
                student.setGrade(grade);
                System.out.println("修改成功！");
                flag = true;
                break;
            }
        }
        if (!flag) {
            System.out.println("要修改成绩的学生不存在！");
        }
    }

    public void queryStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要查询成绩的学生学号：");
        String id = scanner.nextLine();
        boolean flag = false;
        for (int i = 0; i < studentList.size(); i++) {
            Student student = studentList.get(i);
            if (student.getId().equals(id)) {
                System.out.println(student.toString());
                flag = true;
                break;
            }
        }
        if (!flag) {
            System.out.println("要查询成绩的学生不存在！");
        }
    }

    public void sortStudent() {
        Collections.sort(studentList);
        System.out.println("按学号排序成功！");
        for (Student student : studentList) {
            System.out.println(student.toString());
        }
    }

    public void menu() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("请选择操作：");
            System.out.println("1.添加学生");
            System.out.println("2.删除学生");
            System.out.println("3.修改成绩");
            System.out.println("4.按学号查询学生");
            System.out.println("5.按学号排序");
            System.out.println("0.退出程序");
            int choice = scanner.nextInt();
            scanner.nextLine(); // 读取多余的换行符
            switch (choice) {
                case 1:
                    addStudent();
                    break;
                case 2:
                    deleteStudent();
                    break;
                case 3:
                    modifyGrade();
                    break;
                case 4:
                    queryStudent();
                    break;
                case 5:
                    sortStudent();
                    break;
                case 0:
                    System.exit(0);
                default:
                    System.out.println("输入有误，请重新输入！");
            }
        }
    }

    public static void main(String[] args) {
        StudentManage studentManage = new StudentManage();
        studentManage.menu();
    }
}

在`main`方法中创建一个`StudentManage`对象，调用`menu`方法即可开始使用学生管理系统。