代码实现:有五个学生，每个学生有3门课的成绩，从键盘输入以上数据 （包括学生号，姓名，三门课成绩），计算出平均成绩，将原有的数据和计算出的平均分数存放在磁盘文件"stud"中。

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import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; import java.util.ArrayList; import java.util.Scanner;   /*有五个学生，每个学生有3门课的成绩，从键盘输入以上数据  （包括学生号，姓名，三门课成绩），计算出平均成绩，将原有的数据和计算出的平均分数存放在磁盘文件"stud"中。*/ public class Test {       public static void main(String[] args) throws IOException {         ArrayList<Student> list = new ArrayList<>();         Scanner sc = new Scanner(System.in);         int count = 1;         while (list.size() < 5) {             Student s = new Student();             System.out.println("请输入第"+count+"位学生的姓名:");             String name = sc.nextLine();             System.out.println("请输入"+count+"位学生的学号:");             String no = sc.nextLine();             System.out.println("请输入"+count+"位学生的语文成绩:");             String ch = sc.nextLine();             System.out.println("请输入"+count+"位学生的英语成绩:");             String eng = sc.nextLine();             System.out.println("请输入"+count+"位学生的数学成绩:");             String ma = sc.nextLine();             double chinese;             double english;             double math;             try {                 chinese = Double.parseDouble(ch);                 english = Double.parseDouble(eng);                 math = Double.parseDouble(ma);                 s.setName(name);                 s.setChinese(chinese);                 s.setEnglish(english);                 s.setNo(no);                 s.setMath(math);                 list.add(s);                 count++;             } catch (NumberFormatException e) {                 System.out.println("您都是输入有误,请重新输入");                 count--;             }         }                   writerStudent(list);     }       public static void writerStudent(ArrayList<Student> list)             throws IOException {         BufferedWriter bos = new BufferedWriter(new FileWriter("stud"));           for (int i = 0; i < list.size(); i++) {             bos.write("姓名:" + list.get(i).getName() + " 学号:" + list.get(i).getNo()                     + " 语文成绩:" + list.get(i).getChinese() + " 数学成绩"                     + list.get(i).getMath() + "英语成绩:" + list.get(i).getEnglish()                     + " 平均成绩:" + list.get(i).getAvg());             bos.newLine();         }         bos.close();     } }