C#を使用したオブジェクトのシーケンス化

/**
 * 
 *         C#                 
 *      StudentRecord    list            ，     
 *      。         ，              ，       
 */

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;


namespace studentRecord
{
    class Program
    {
        static void Main(string[] args)
        {

            Student s1 = new Student();
            s1.id = "20081120029";
            s1.name = "  ";
            s1.major = "  ";
            s1.phone = "12345678";
            s1.sex = " ";
            s1.email = "[email protected]";

            Student s2 = new Student();
            s2.id = "20081120030";
            s2.name = "   ";
            s2.major = "  ";
            s2.phone = "1234567889";
            s2.sex = " ";
            s2.email = "[email protected]";

            string path = "record.dat";

            StudentRecord sr = new StudentRecord();


            Console.WriteLine("      
{0}", s1.ToString());
            Console.WriteLine("      
{0}", s2.ToString());
            sr.Add(s1, path); //      
            sr.Add(s2, path);
            Console.WriteLine("      ");

            Console.WriteLine("-------------------------------");

            Console.WriteLine("       20081120029   ");
            Student s = sr.Search("20081120029", path);
            Console.WriteLine("         
{0}", s.ToString());


            Console.WriteLine("-------------------------------");


            Console.WriteLine("    20081120029     ");
            s.major = "  ";
            s.email = "[email protected]";
            sr.Update(s, path); //    

            s = sr.Search("20081120029", path);
            Console.WriteLine("     20081120029      
{0}", s.ToString());

            Console.WriteLine("-------------------------------");


            Console.WriteLine("    20081120029   
");
            sr.Delete("20081120029", path);
            List<Student> list = sr.GetAll(path);
            Console.WriteLine("       
");
            foreach (Student sn in list)
            {
                Console.WriteLine("{0}", sn.ToString());
            }

            if (File.Exists(path))  //             ，      
            {
                File.Delete(path);
            }

            Console.ReadKey();
        }
    }

    [Serializable]  //           
    class Student {

        public string email { set; get; }
        public string name { set; get; }
        public string id { set; get; }
        public string sex { set; get; }
        public string birth { set; get; }
        public string phone { set; get; }
        public string major { set; get; }

        public override string ToString()
        {
            return "  ：" + this.id + ",
" + "  ：" + this.name + ",
" + "  ：" + this.sex + ",
" + "    ：" + this.birth + ",
" + "  ：" + this.major + ",
" + "    ：" + this.phone + ",
" + "email：" + this.email + ",
";
        }

    }

    class StudentRecord
    {
        private IFormatter formatter;
        private Stream stream;
        private List<Student> list;

        public StudentRecord()
        {
            formatter = new BinaryFormatter();
        }

        public List<Student> GetAll(string path)
        {
            OpenFileForRead(path);
            return list;
        }

        public void Add(Student st,string path)
        {
            OpenFileForRead(path);
            if (list == null)
            {
                list = new List<Student>();
                list.Add(st);
                OpenFileForWrite(path);  //        
                return;
            }else {
                list.Add(st);
                OpenFileForWrite(path);  //        
                return;
            }
        }

        public void Update(Student st,string path)
        {
            OpenFileForRead(path);
            if (list == null)
            {
                list = new List<Student>();
                list.Add(st);
                OpenFileForWrite(path);  //        
            }
            else
            {
                for(int i=0;i<list.Count;i++)
                {
                    if (list[i].id.Equals(st.id))
                    {
                        list.RemoveAt(i);  //     
                        list.Add(st); //           
                        break;
                    }
                }
            }
            OpenFileForWrite(path); //        
        }

        public void Delete(string id,string path)
        {
            OpenFileForRead(path);
            if (list == null)
            {
                Console.WriteLine("       ");
                return;
            }
            else
            {
                for (int i = 0; i < list.Count; i++)
                {
                    if (list[i].id.Equals(id)) //    
                    {
                        list.RemoveAt(i);  //    
                        break;
                    }
                }
                OpenFileForWrite(path); //     
            }
        }

        public Student Search(string id, string path)
        {
            Student s= null;
            OpenFileForRead(path);
            if (list == null || list.Count == 0)
            {
                Console.WriteLine("       ");
                return null;
            }else
            {
                foreach (Student st in list)
                {
                    if (st.id.Equals(id)) //  id
                    {
                        s = st;    //          
                        return s;  
                    }
  
                }
            }
            return null;
        }

        private void OpenFileForRead(string path)
        {
            if (File.Exists(path)) //         
            {
                stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);  //          
                this.list = (List<Student>)formatter.Deserialize(stream); //     
                stream.Close();
            }
            else
            {
                this.list = null;
            }
        }

        private void OpenFileForWrite(string path)
        {
            stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None);
            formatter.Serialize(stream, this.list);
            stream.Close();
        }
    }
}