根据以下这段话写出相对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。

以下是三个类的代码实现：

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;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public String getPhone() {
        return phone;
    }

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

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

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

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

StudentUtils.java

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

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

    public static void addStudent(Student student) {
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(fileName, true));
            writer.write(student.getId() + "," + student.getName() + "," + student.getAddress() + "," + student.getPhone());
            writer.newLine();
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void deleteStudent(String id) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader(fileName));
            ArrayList<String> lines = new ArrayList<>();
            String line;
            while ((line = reader.readLine()) != null) {
                if (!line.startsWith(id + ",")) {
                    lines.add(line);
                }
            }
            reader.close();
            BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
            for (String l : lines) {
                writer.write(l);
                writer.newLine();
            }
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void modifyStudent(String id, Student newStudent) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader(fileName));
            ArrayList<String> lines = new ArrayList<>();
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.startsWith(id + ",")) {
                    line = newStudent.getId() + "," + newStudent.getName() + "," + newStudent.getAddress() + "," + newStudent.getPhone();
                }
                lines.add(line);
            }
            reader.close();
            BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
            for (String l : lines) {
                writer.write(l);
                writer.newLine();
            }
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Student queryStudent(String id) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader(fileName));
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.startsWith(id + ",")) {
                    String[] fields = line.split(",");
                    return new Student(fields[0], fields[1], fields[2], fields[3]);
                }
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

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("0.退出程序");
            int choice = scanner.nextInt();
            scanner.nextLine();
            switch (choice) {
                case 1:
                    System.out.print("请输入学生学号：");
                    String id = scanner.nextLine();
                    System.out.print("请输入学生姓名：");
                    String name = scanner.nextLine();
                    System.out.print("请输入学生家庭住址：");
                    String address = scanner.nextLine();
                    System.out.print("请输入学生电话号码：");
                    String phone = scanner.nextLine();
                    Student newStudent = new Student(id, name, address, phone);
                    StudentUtils.addStudent(newStudent);
                    System.out.println("新增学生信息成功！");
                    break;
                case 2:
                    System.out.print("请输入要删除的学生学号：");
                    id = scanner.nextLine();
                    StudentUtils.deleteStudent(id);
                    System.out.println("删除学生信息成功！");
                    break;
                case 3:
                    System.out.print("请输入要修改的学生学号：");
                    id = scanner.nextLine();
                    Student student = StudentUtils.queryStudent(id);
                    if (student != null) {
                        System.out.print("请输入新的学生学号：");
                        String newId = scanner.nextLine();
                        System.out.print("请输入新的学生姓名：");
                        name = scanner.nextLine();
                        System.out.print("请输入新的学生家庭住址：");
                        address = scanner.nextLine();
                        System.out.print("请输入新的学生电话号码：");
                        phone = scanner.nextLine();
                        newStudent = new Student(newId, name, address, phone);
                        StudentUtils.modifyStudent(id, newStudent);
                        System.out.println("修改学生信息成功！");
                    } else {
                        System.out.println("学生信息不存在！");
                    }
                    break;
                case 4:
                    System.out.print("请输入要查询的学生学号：");
                    id = scanner.nextLine();
                    student = StudentUtils.queryStudent(id);
                    if (student != null) {
                        System.out.println("学号：" + student.getId());
                        System.out.println("姓名：" + student.getName());
                        System.out.println("家庭住址：" + student.getAddress());
                        System.out.println("电话号码：" + student.getPhone());
                    } else {
                        System.out.println("学生信息不存在！");
                    }
                    break;
                case 0:
                    System.out.println("程序已退出。");
                    System.exit(0);
                    break;
                default:
                    System.out.println("请输入正确的操作编号！");
                    break;
            }
        }
    }
}