根据以下这段话写出代码文件夹中有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。

以下是实现上述功能的三个类文件：

Student.java

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

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

    // getters and setters
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
}

StudentUtils.java

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

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

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

    public static void deleteStudent(String id) {
        List<Student> students = readFromFile();
        for (int i = 0; i < students.size(); i++) {
            if (students.get(i).getId().equals(id)) {
                students.remove(i);
                break;
            }
        }
        writeToFile(students);
    }

    public static void updateStudent(Student student) {
        List<Student> students = readFromFile();
        for (int i = 0; i < students.size(); i++) {
            if (students.get(i).getId().equals(student.getId())) {
                students.set(i, student);
                break;
            }
        }
        writeToFile(students);
    }

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

    public static List<Student> getAllStudents() {
        return readFromFile();
    }

    private static List<Student> readFromFile() {
        List<Student> students = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] parts = line.split(",");
                Student student = new Student(parts[0], parts[1], parts[2], parts[3]);
                students.add(student);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return students;
    }

    private static void writeToFile(List<Student> students) {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(FILE_NAME))) {
            for (Student student : students) {
                writer.write(student.getId() + "," + student.getName() + "," + student.getAddress() + "," + student.getPhone());
                writer.newLine();
            }
        } catch (IOException 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");
            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    addStudent(scanner);
                    break;
                case 2:
                    deleteStudent(scanner);
                    break;
                case 3:
                    updateStudent(scanner);
                    break;
                case 4:
                    getStudent(scanner);
                    break;
                case 5:
                    System.exit(0);
                    break;
                default:
                    System.out.println("无效操作，请重新选择！");
                    break;
            }
        }
    }

    private static void addStudent(Scanner scanner) {
        System.out.println("请输入学生学号：");
        String id = scanner.next();
        System.out.println("请输入学生姓名：");
        String name = scanner.next();
        System.out.println("请输入学生家庭住址：");
        String address = scanner.next();
        System.out.println("请输入学生电话号码：");
        String phone = scanner.next();
        Student student = new Student(id, name, address, phone);
        StudentUtils.addStudent(student);
        System.out.println("新增学生信息成功！");
    }

    private static void deleteStudent(Scanner scanner) {
        System.out.println("请输入要删除的学生学号：");
        String id = scanner.next();
        StudentUtils.deleteStudent(id);
        System.out.println("删除学生信息成功！");
    }

    private static void updateStudent(Scanner scanner) {
        System.out.println("请输入要修改的学生学号：");
        String id = scanner.next();
        Student student = StudentUtils.getStudent(id);
        if (student == null) {
            System.out.println("未找到学生信息！");
            return;
        }
        System.out.println("请输入学生姓名：");
        String name = scanner.next();
        System.out.println("请输入学生家庭住址：");
        String address = scanner.next();
        System.out.println("请输入学生电话号码：");
        String phone = scanner.next();
        student.setName(name);
        student.setAddress(address);
        student.setPhone(phone);
        StudentUtils.updateStudent(student);
        System.out.println("修改学生信息成功！");
    }

    private static void getStudent(Scanner scanner) {
        System.out.println("请输入要查询的学生学号：");
        String id = scanner.next();
        Student student = StudentUtils.getStudent(id);
        if (student == null) {
            System.out.println("未找到学生信息！");
            return;
        }
        System.out.println("学生学号：" + student.getId());
        System.out.println("学生姓名：" + student.getName());
        System.out.println("学生家庭住址：" + student.getAddress());
        System.out.println("学生电话号码：" + student.getPhone());
    }
}