根据以下这段话写出相应的代码文件夹中有3个类文件（.java文件），Student.java StudentUtils.java StudentManager.java 学生管理系统 1.学生实体用Student类，包含学生学号，姓名，家庭住址，电话号码 2.学生操作用StudentUtils类，包含学生信息的新增，删除，修改，查询，保存 -每次新增学生时，要将学生信息保存到文件中 -每次删除学生时，要将相应学生信息从文件中删除 -每次修改学生时，要将相应学生信息在文件中修改 -学生信息保存在StudentInfo.txt中 3.学生管理用StudentManager类 当程序运行后，出现菜单供使用者选择 新增学生信息， 删除学生信息， 修改学生信息， 查询学生信息。

以下是对应的代码：

Student.java

public class Student {
    private String id;
    private String name;
    private String address;
    private String phoneNumber;

    public Student(String id, String name, String address, String phoneNumber) {
        this.id = id;
        this.name = name;
        this.address = address;
        this.phoneNumber = phoneNumber;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }
}

StudentUtils.java

import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class StudentUtils {
    private static final String FILE_PATH = "StudentInfo.txt";

    public static void addStudent(Student student) {
        List<Student> students = getAllStudents();
        students.add(student);
        saveStudents(students);
    }

    public static void deleteStudent(String id) {
        List<Student> students = getAllStudents();
        students.removeIf(student -> student.getId().equals(id));
        saveStudents(students);
    }

    public static void modifyStudent(Student student) {
        List<Student> students = getAllStudents();
        int index = -1;
        for (int i = 0; i < students.size(); i++) {
            if (students.get(i).getId().equals(student.getId())) {
                index = i;
                break;
            }
        }
        if (index != -1) {
            students.set(index, student);
            saveStudents(students);
        }
    }

    public static Student getStudent(String id) {
        List<Student> students = getAllStudents();
        for (Student student : students) {
            if (student.getId().equals(id)) {
                return student;
            }
        }
        return null;
    }

    public static List<Student> getAllStudents() {
        List<Student> students = new ArrayList<>();
        File file = new File(FILE_PATH);
        if (!file.exists()) {
            return students;
        }

        try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] fields = line.split(",");
                if (fields.length == 4) {
                    students.add(new Student(fields[0], fields[1], fields[2], fields[3]));
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return students;
    }

    private static void saveStudents(List<Student> students) {
        File file = new File(FILE_PATH);
        try (PrintWriter writer = new PrintWriter(file)) {
            for (Student student : students) {
                writer.println(String.format("%s,%s,%s,%s", student.getId(), student.getName(),
                        student.getAddress(), student.getPhoneNumber()));
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

StudentManager.java

import java.util.Scanner;

public class StudentManager {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("请选择操作：");
            System.out.println("1.新增学生信息");
            System.out.println("2.删除学生信息");
            System.out.println("3.修改学生信息");
            System.out.println("4.查询学生信息");
            System.out.println("5.退出程序");
            int choice = scanner.nextInt();
            scanner.nextLine();

            switch (choice) {
                case 1:
                    System.out.println("请输入学生信息（学号,姓名,家庭住址,电话号码）：");
                    String[] fields = scanner.nextLine().split(",");
                    if (fields.length == 4) {
                        StudentUtils.addStudent(new Student(fields[0], fields[1], fields[2], fields[3]));
                    }
                    break;
                case 2:
                    System.out.println("请输入学生学号：");
                    String id = scanner.nextLine();
                    StudentUtils.deleteStudent(id);
                    break;
                case 3:
                    System.out.println("请输入学生信息（学号,姓名,家庭住址,电话号码）：");
                    fields = scanner.nextLine().split(",");
                    if (fields.length == 4) {
                        StudentUtils.modifyStudent(new Student(fields[0], fields[1], fields[2], fields[3]));
                    }
                    break;
                case 4:
                    System.out.println("请输入学生学号：");
                    id = scanner.nextLine();
                    Student student = StudentUtils.getStudent(id);
                    if (student != null) {
                        System.out.println(String.format("学号：%s，姓名：%s，家庭住址：%s，电话号码：%s",
                                student.getId(), student.getName(), student.getAddress(), student.getPhoneNumber()));
                    } else {
                        System.out.println("未找到该学生信息！");
                    }
                    break;
                case 5:
                    return;
                default:
                    System.out.println("无效的操作，请重新选择！");
            }
        }
    }
}