运用java，写一个学生学籍管理系统，能够实现添加，删除，查找，修改，统计学生成绩到数据文件，计算平均成绩，计算合格率的功能，

以下是一个简单的学生学籍管理系统的Java代码，包括添加、删除、查找、修改、统计学生成绩到数据文件、计算平均成绩、计算合格率的功能：

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

public class StudentManagementSystem {

    private List<Student> students;

    public StudentManagementSystem() {
        students = new ArrayList<>();
    }

    public void addStudent(Student student) {
        students.add(student);
    }

    public void removeStudent(Student student) {
        students.remove(student);
    }

    public Student findStudent(String id) {
        for (Student student : students) {
            if (student.getId().equals(id)) {
                return student;
            }
        }
        return null;
    }

    public void updateStudent(Student student) {
        for (int i = 0; i < students.size(); i++) {
            if (students.get(i).getId().equals(student.getId())) {
                students.set(i, student);
                return;
            }
        }
    }

    public void saveToFile(String fileName) {
        try {
            ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(fileName));
            out.writeObject(students);
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void loadFromFile(String fileName) {
        try {
            ObjectInputStream in = new ObjectInputStream(new FileInputStream(fileName));
            students = (List<Student>) in.readObject();
            in.close();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public double getAverageScore() {
        double sum = 0;
        for (Student student : students) {
            sum += student.getScore();
        }
        return sum / students.size();
    }

    public double getPassRate() {
        int passCount = 0;
        for (Student student : students) {
            if (student.isPass()) {
                passCount++;
            }
        }
        return (double) passCount / students.size();
    }

    public static void main(String[] args) {
        StudentManagementSystem system = new StudentManagementSystem();
        system.loadFromFile("students.dat");

        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. 查找学生");
            System.out.println("4. 修改学生");
            System.out.println("5. 统计学生成绩到数据文件");
            System.out.println("6. 计算平均成绩");
            System.out.println("7. 计算合格率");
            System.out.println("0. 退出");
            System.out.print("> ");
            int choice = scanner.nextInt();
            scanner.nextLine();

            switch (choice) {
                case 1:
                    System.out.print("请输入学号：");
                    String id = scanner.nextLine();
                    System.out.print("请输入姓名：");
                    String name = scanner.nextLine();
                    System.out.print("请输入成绩：");
                    double score = scanner.nextDouble();
                    scanner.nextLine();
                    Student student = new Student(id, name, score);
                    system.addStudent(student);
                    System.out.println("添加成功！");
                    break;
                case 2:
                    System.out.print("请输入学号：");
                    id = scanner.nextLine();
                    student = system.findStudent(id);
                    if (student != null) {
                        system.removeStudent(student);
                        System.out.println("删除成功！");
                    } else {
                        System.out.println("查无此人！");
                    }
                    break;
                case 3:
                    System.out.print("请输入学号：");
                    id = scanner.nextLine();
                    student = system.findStudent(id);
                    if (student != null) {
                        System.out.println(student);
                    } else {
                        System.out.println("查无此人！");
                    }
                    break;
                case 4:
                    System.out.print("请输入学号：");
                    id = scanner.nextLine();
                    student = system.findStudent(id);
                    if (student != null) {
                        System.out.print("请输入姓名：");
                        name = scanner.nextLine();
                        System.out.print("请输入成绩：");
                        score = scanner.nextDouble();
                        scanner.nextLine();
                        student.setName(name);
                        student.setScore(score);
                        system.updateStudent(student);
                        System.out.println("修改成功！");
                    } else {
                        System.out.println("查无此人！");
                    }
                    break;
                case 5:
                    System.out.print("请输入文件名：");
                    String fileName = scanner.nextLine();
                    system.saveToFile(fileName);
                    System.out.println("保存成功！");
                    break;
                case 6:
                    double averageScore = system.getAverageScore();
                    System.out.println("平均成绩为：" + averageScore);
                    break;
                case 7:
                    double passRate = system.getPassRate();
                    System.out.println("合格率为：" + passRate);
                    break;
                case 0:
                    system.saveToFile("students.dat");
                    System.out.println("退出成功！");
                    return;
            }
        }
    }
}

class Student implements Serializable {

    private String id;
    private String name;
    private double score;

    public Student(String id, String name, double score) {
        this.id = id;
        this.name = name;
        this.score = score;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getScore() {
        return score;
    }

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

    public void setScore(double score) {
        this.score = score;
    }

    public boolean isPass() {
        return score >= 60;
    }

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