Hi,

I have read out one sample online article about Interface & Abstract Class. In that article all are mentioned in good way and easily understandable but I have a problem in understanding following code.

Article Link :
http://www.codeproject.com/csharp/A...SInterfaces.asp

In Following code, Lines which are marked by RED color its not understandablel by me.

In short , in first function why we need to use Casting and while in second function why we dont need to use casting.

Can you please help me out for this ?

Code :

private void InterfaceExample_Click(object sender,
System.EventArgs e)
{
try
{

IEmployee emp;

Emp_fulltime2 emp1 = new Emp_fulltime2();
//has to be casted because of the interface!
emp = (IEmployee) emp1;
emp.ID = "2234";
emp.FirstName= "Rahman" ;
emp.LastName = "Mahmoodi" ;
//call add method od the object
MessageBox.Show(emp.Add().ToString());

//call the CalculateWage method
MessageBox.Show(emp.CalculateWage().ToString());


}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}

}

private void cmdAbstractExample_Click(object sender,
System.EventArgs e)
{

Employee emp;
//no casting is requird!
emp = new Emp_Fulltime();

emp.ID = "2244";
emp.FirstName= "Maria" ;
emp.LastName = "Robinlius" ;
MessageBox.Show(emp.Add().ToString());

//call the CalculateWage method
MessageBox.Show(emp.CalculateWage().ToString());

}

Thanks,
Hiren Patel