finish PointOfSaleApp

src/main/java/edu/ubu/csapp/PointOfSaleApp.java

 package edu.ubu.csapp;
 
-import java.util.Scanner;
+import java.io.*;
+import java.util.*;
 
 public class PointOfSaleApp {
 
@@ -11,6 +12,7 @@ public class PointOfSaleApp {
         int n = s.nextInt();
         s.nextLine();
 
+        ArrayList<Product> products = new ArrayList<>();
         for (int i=0; i<n; i++) {
             System.out.printf("ชื่อสินค้า #%d: ", i+1);
             String desc = s.nextLine();
@@ -19,6 +21,28 @@ public class PointOfSaleApp {
             System.out.printf("จำนวนชิ้นของสินค้า #%d: ", i+1);
             int unit = s.nextInt();
             s.nextLine();
+            products.add(new Product(desc, price, unit));
+        }
+        saveLongFile(products);
+        ArrayList<Product> db = loadFromFile();
+    }
+
+    private static ArrayList<Product> loadFromFile() {
+        String fname = "products.db";
+        ArrayList<Product> products = new ArrayList<>();
+        try (ObjectInputStream oos = new ObjectInputStream(new FileInputStream(fname))) {
+            products = (ArrayList<Product>)oos.readObject();
+            return products;
+        } catch (Exception e) {
+        }
+        return products;
+    }
+
+    private static void saveLongFile(ArrayList<Product> products) {
+        String fname = "products.db";
+        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(fname))) {
+            oos.writeObject(products);
+        } catch (Exception e) {
         }
     }