vb.net - serialization in c# calling methods -

this code book "network programming in .net using c# , vb.net"

what dont understand how _issuancedate,_deliverydate,_invoicedate,_paymentdate being set. in code there no explicit setting of value , yet xml file contains dates of all, , how purchaseorder class methods getting called ?

    using system;     using system.collections.generic;     using system.componentmodel;     using system.data;     using system.drawing;     using system.linq;     using system.text;     using system.windows.forms;     using system.runtime.serialization.formatters.soap;     using system.runtime.serialization.formatters.binary;     using system.io;      namespace serialization     {          public partial class form1 : form          {     public form1()     {         initializecomponent();     }      private void form1_load(object sender, eventargs e)     {      }      private void button1_click(object sender, eventargs e)     {         company vendor = new company();         company buyer = new company();         lineitem goods = new lineitem();         purchaseorder po = new purchaseorder();          vendor.name = "acme";         buyer.name = "wiley e coyete";          goods.description = "anti road runner gun";         goods.quantity = 1;         goods.cost = 599.99;          po.items = new lineitem[1];         po.items[0] = goods;         po.buyer = buyer;         po.vendor = vendor;            soapformatter sf = new soapformatter();         filestream fs = file.create("c:\\users\\s ghosh\\desktop\\po.xml");         sf.serialize(fs, po);         fs.close();                 }      private void button2_click(object sender, eventargs e)     {         soapformatter sf = new soapformatter();         filestream fs = file.openread("c:\\users\\s ghosh\\desktop\\po.xml");         purchaseorder po = (purchaseorder)sf.deserialize(fs);         fs.close();         messagebox.show("customer " + po.buyer.name);         po.show();     } }  public enum purchaseorderstates {      delivered,     issued,     invoiced,     paid }  [serializable()] public class company {     public string name;     public string address;     public string phone; }  [serializable()] public class lineitem {     public string description;     public int quantity;     public double cost; } [serializable()] public class purchaseorder {     private purchaseorderstates _purchaseorderstatus;     private datetime _issuancedate;     private datetime _deliverydate;     private datetime _invoicedate;     private datetime _paymentdate;      public company buyer;     public company vendor;     public company reference;      public lineitem[] items;     public purchaseorder()     {         _purchaseorderstatus = purchaseorderstates.issued;         _issuancedate = datetime.now;     }      public void recorddelivery()     {         if (_purchaseorderstatus == purchaseorderstates.issued)         {             _purchaseorderstatus = purchaseorderstates.delivered;             _deliverydate = datetime.now;         }     }      public void recordinvoice()     {         if (_purchaseorderstatus == purchaseorderstates.delivered)         {             _purchaseorderstatus = purchaseorderstates.invoiced;             _invoicedate = datetime.now;         }     }      public void recordpayment()     {         if (_purchaseorderstatus == purchaseorderstates.invoiced)         {             _purchaseorderstatus = purchaseorderstates.paid;             _issuancedate = datetime.now;         }     } } 

}

_issuancedate set in purchaseorder constructor

_issuancedate = datetime.now; 

all other dates go default values.