Have anyone try to use default parameter function?

yes, i have try out it and i got the answer. it is simple overloading mechanism and c# complier call parameter less mathode first. it will not give any error. work fine.
thanks

So does anyone know a way to force the use of the method with the default parameter?

I thought of a solution with a special delegate for this case - But this doesn't work like I first thought: look how this behaves...

class Program
 {
     delegate void methodDelegate(string str = "ABC");

     static void Main()
     {
         method();
         methodDelegate methodWithOptionalParameter = method;
         methodWithOptionalParameter.Invoke();

         Console.ReadKey();
     }

     static void method(string str = "XYZ")
     {
         Console.WriteLine("method(string str = \"{0}\")", str);

     }

     static void method()
     {
         Console.WriteLine("method()");
     }

 }

(hint: it uses the default value from the delegate Definition)

If you're interviewing for a programming job, and it never occurred to you to try it yourself and see, do you honestly think you've selected an appropriate career path?

Create a console application and run this code to see which method is being called.

using System;

class Program
{

    static void Main()
    {
        method();
        Console.ReadLine();
    }

    static void method(string str = "")
    {
        Console.WriteLine("method(string str = \"\")");

    }

    static void method()
    {
        Console.WriteLine("method()");
    }
}