System IO C# by API

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Soap;
class SoapTest
{
   public static void Main()
   {
      SerialEmployee emp1 = new SerialEmployee();
      SerialEmployee emp2 = new SerialEmployee();
      emp1.EmployeeID = 1;
      emp1.LastName = "B";
      emp1.FirstName = "K";
      emp1.YearsService = 12;
      emp1.Salary = 35000.50;
      emp2.EmployeeID = 2;
      emp2.LastName = "B";
      emp2.FirstName = "J";
      emp2.YearsService = 9;
      emp2.Salary = 23700.30;
      Stream str = new FileStream("soaptest.xml", FileMode.Create, FileAccess.ReadWrite);
      IFormatter formatter = new SoapFormatter();
      formatter.Serialize(str, emp1);
      formatter.Serialize(str, emp2);
      str.Close();
   }
}
[Serializable]
public class SerialEmployee
{
   public int EmployeeID;
   public string LastName;
   public string FirstName;
   public int YearsService;
   public double Salary;
   public SerialEmployee()
   {
      EmployeeID = 0;
      LastName = null;
      FirstName = null;
      YearsService = 0;
      Salary = 0.0;
   }
}