将Student对象(属性：int id, String name(不多于10个字符),int age,double grade)写入文件、读出文件，分别尝试使用以下方式实现： (1)DataInputStream, DataOutputStream； (2)Scanner(或BufferedReader), PrintWriter； (3)ObjectInputStream, ObjectOutputStream。 问题：1、2、3方法生成的文件大小各是多少？尝试分析1和2输出的文件大小。 要求：以方法的形式进行封装（使用方法重载），例如： public static void writeStudent(Student s, DataOutputStream dos){}; 或者：public static void writeStudent(List stus, DataOutputStream dos){}; 读取时类似： public static Student readStudent(DataInputStream dis){}; 或者：public static List readStudent(DataInputStream dis){};

以下是实现以上要求的代码：

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

public class Student {
    private int id;
    private String name;
    private int age;
    private double grade;

    public Student(int id, String name, int age, double grade) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.grade = grade;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public double getGrade() {
        return grade;
    }

    public static void writeStudent(Student s, DataOutputStream dos) throws IOException {
        dos.writeInt(s.getId());
        dos.writeUTF(s.getName());
        dos.writeInt(s.getAge());
        dos.writeDouble(s.getGrade());
    }

    public static void writeStudent(List<Student> stus, DataOutputStream dos) throws IOException {
        dos.writeInt(stus.size());
        for (Student s : stus) {
            writeStudent(s, dos);
        }
    }

    public static Student readStudent(DataInputStream dis) throws IOException {
        int id = dis.readInt();
        String name = dis.readUTF();
        int age = dis.readInt();
        double grade = dis.readDouble();
        return new Student(id, name, age, grade);
    }

    public static List<Student> readStudents(DataInputStream dis) throws IOException {
        List<Student> stus = new ArrayList<>();
        int num = dis.readInt();
        for (int i = 0; i < num; i++) {
            stus.add(readStudent(dis));
        }
        return stus;
    }

    public static void writeStudent(Student s, PrintWriter pw) {
        pw.println(s.getId());
        pw.println(s.getName());
        pw.println(s.getAge());
        pw.println(s.getGrade());
    }

    public static void writeStudent(List<Student> stus, PrintWriter pw) {
        pw.println(stus.size());
        for (Student s : stus) {
            writeStudent(s, pw);
        }
    }

    public static Student readStudent(Scanner scanner) {
        int id = scanner.nextInt();
        String name = scanner.next();
        int age = scanner.nextInt();
        double grade = scanner.nextDouble();
        return new Student(id, name, age, grade);
    }

    public static List<Student> readStudents(Scanner scanner) {
        List<Student> stus = new ArrayList<>();
        int num = scanner.nextInt();
        for (int i = 0; i < num; i++) {
            stus.add(readStudent(scanner));
        }
        return stus;
    }

    public static void writeStudent(Student s, ObjectOutputStream oos) throws IOException {
        oos.writeObject(s);
    }

    public static void writeStudent(List<Student> stus, ObjectOutputStream oos) throws IOException {
        oos.writeObject(stus);
    }

    public static Student readStudent(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        return (Student) ois.readObject();
    }

    public static List<Student> readStudents(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        return (List<Student>) ois.readObject();
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        List<Student> stus = new ArrayList<>();
        stus.add(new Student(1, "Tom", 18, 90));
        stus.add(new Student(2, "Jerry", 19, 80));
        stus.add(new Student(3, "Mike", 20, 70));

        // 使用DataInputStream, DataOutputStream
        FileOutputStream fos1 = new FileOutputStream("data1.txt");
        DataOutputStream dos1 = new DataOutputStream(fos1);
        writeStudent(stus, dos1);
        dos1.close();
        FileInputStream fis1 = new FileInputStream("data1.txt");
        DataInputStream dis1 = new DataInputStream(fis1);
        List<Student> stus1 = readStudents(dis1);
        dis1.close();

        // 使用Scanner(或BufferedReader), PrintWriter
        FileOutputStream fos2 = new FileOutputStream("data2.txt");
        PrintWriter pw2 = new PrintWriter(fos2);
        writeStudent(stus, pw2);
        pw2.close();
        FileInputStream fis2 = new FileInputStream("data2.txt");
        Scanner scanner2 = new Scanner(fis2);
        List<Student> stus2 = readStudents(scanner2);
        scanner2.close();

        // 使用ObjectInputStream, ObjectOutputStream
        FileOutputStream fos3 = new FileOutputStream("data3.txt");
        ObjectOutputStream oos3 = new ObjectOutputStream(fos3);
        writeStudent(stus, oos3);
        oos3.close();
        FileInputStream fis3 = new FileInputStream("data3.txt");
        ObjectInputStream ois3 = new ObjectInputStream(fis3);
        List<Student> stus3 = readStudents(ois3);
        ois3.close();

        System.out.println("stus1: " + stus1);
        System.out.println("stus2: " + stus2);
        System.out.println("stus3: " + stus3);

        File file1 = new File("data1.txt");
        System.out.println("data1.txt size: " + file1.length() + " bytes");
        File file2 = new File("data2.txt");
        System.out.println("data2.txt size: " + file2.length() + " bytes");
        File file3 = new File("data3.txt");
        System.out.println("data3.txt size: " + file3.length() + " bytes");
    }
}

上述代码中，使用了方法重载的形式，可以根据需要选择不同的方法进行读写操作。在main方法中，我们首先创建了一个包含三个学生的List对象stus，并分别使用DataInputStream、Scanner和ObjectInputStream进行写入文件操作，然后再使用相应的读取方式将文件中的数据读取出来并存入新的List对象中。最后，我们输出了三个List对象以及生成的三个文件的大小。需要注意的是，在使用DataInputStream和PrintWriter进行读写操作时，需要使用相应的流对象的close方法关闭流，而在使用ObjectInputStream和ObjectOutputStream进行读写操作时，不需要手动关闭流对象，因为它们会在读写完成后自动关闭。