编程练习 请老师帮忙完善一下代码

Product

package com.lding.io;

import java.io.Serializable;

public class Product implements Serializable {
    private int id;
    private String name;
    private String categories;
    private double price;
    public Product(){

    }

    public Product(int id, String name, String categories, double price) {
        this.id = id;
        this.name = name;
        this.categories = categories;
        this.price = price;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getCategories() {
        return categories;
    }

    public void setCategories(String categories) {
        this.categories = categories;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "产品ID:" + id +
                "\n产品名称:" + name  +
                "\n产品属性:" + categories +
                "\n产品价格:" + price +
                "元\n";
    }
}

ProductTest

​package com.lding.io;

import java.io.*;

public class ProductTest {
    public static void main(String[] args) {
        Product iphone= new Product(123,"iphone","telephone",4888.0);
        Product ipad=new Product(234,"ipad","computer",5088.0);
        Product macbook=new Product(345,"macbook","computer",10688.0);
        Product iwatch=new Product(256,"iwatch","watch",4799.0);
        FileInputStream fis=null;
        ObjectInputStream ois=null;
        FileOutputStream fos=null;
        ObjectOutputStream oos=null;
        try {
             fis=new FileInputStream("lding.txt");
             ois=new ObjectInputStream(fis);

             fos=new FileOutputStream("lding.txt");
             oos=new ObjectOutputStream(fos);

            oos.writeObject(iphone);
            oos.writeObject(ipad);
            oos.writeObject(macbook);
            oos.writeObject(iwatch);
            oos.flush();

            System.out.println("apple系列产品信息");
            Product temp=(Product) ois.readObject();
            System.out.println(temp);
            temp=(Product) ois.readObject();
            System.out.println(temp);
            temp=(Product) ois.readObject();
            System.out.println(temp);
            temp=(Product) ois.readObject();
            System.out.println(temp);

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            try {
                fis.close();
                fos.close();
                oos.close();
                ois.close();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }
}