JAVA语言编写一个学生成绩管理程序，内容包括学号、姓名以及数学、外语、Java等课程的成绩，设计一个文件管理程序，实现如下功能: ①录入10个学生的数据，写入文件。 ② 从文件中读取数据，计算每位学生的所有课程平均分。③ 计算全部学生的数学平均分。

好的，我会根据您的要求进行回答，以下是JAVA语言编写一个学生成绩管理程序的代码：

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

class Student {
    String id;
    String name;
    float mathScore;
    float englishScore;
    float javaScore;

    public Student(String id, String name, float mathScore, float englishScore, float javaScore) {
        this.id = id;
        this.name = name;
        this.mathScore = mathScore;
        this.englishScore = englishScore;
        this.javaScore = javaScore;
    }

    public float getAverageScore() {
        return (mathScore + englishScore + javaScore) / 3;
    }
}

public class StudentManagement {
    public static void main(String[] args) {
        List<Student> students = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        // 录入10个学生的数据，写入文件
        for (int i = 0; i < 10; i++) {
            System.out.println("请输入第" + (i + 1) + "个学生的信息");

            System.out.println("学号：");
            String id = scanner.next();

            System.out.println("姓名：");
            String name = scanner.next();

            System.out.println("数学成绩：");
            float mathScore = scanner.nextFloat();

            System.out.println("外语成绩：");
            float englishScore = scanner.nextFloat();

            System.out.println("Java成绩：");
            float javaScore = scanner.nextFloat();

            Student student = new Student(id, name, mathScore, englishScore, javaScore);
            students.add(student);
        }

        try {
            File file = new File("students.txt");
            FileWriter fileWriter = new FileWriter(file);

            for (Student student : students) {
                fileWriter.write(student.id + " " + student.name + " " + student.mathScore + " " + student.englishScore + " " + student.javaScore + "\n");
            }

            fileWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 从文件中读取数据，计算每位学生的所有课程平均分
        try {
            File file = new File("students.txt");
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader = new BufferedReader(fileReader);

            String line;
            while ((line = bufferedReader.readLine()) != null) {
                String[] values = line.split(" ");
                String id = values[0];
                String name = values[1];
                float mathScore = Float.parseFloat(values[2]);
                float englishScore = Float.parseFloat(values[3]);
                float javaScore = Float.parseFloat(values[4]);

                Student student = new Student(id, name, mathScore, englishScore, javaScore);
                float averageScore = student.getAverageScore();
                System.out.println(student.name + "的平均分是：" + averageScore);
            }

            bufferedReader.close();
            fileReader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 计算全部学生的数学平均分
        float totalMathScore = 0;
        int count = 0;

        try {
            File file = new File("students.txt");
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader = new BufferedReader(fileReader);

            String line;
            while ((line = bufferedReader.readLine()) != null) {
                String[] values = line.split(" ");
                float mathScore = Float.parseFloat(values[2]);
                totalMathScore += mathScore;
                count++;
            }

            bufferedReader.close();
            fileReader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        float averageMathScore = totalMathScore / count;
        System.out.println("全部学生的数学平均分是：" + averageMathScore);
    }
}

这个程序可以实现您提出的三个功能：

1. 录入10个学生的数据，写入文件。
2. 从文件中读取数据，计算每位学生的所有课程平均分。
3. 计算全部学生的数学平均分。