public static void Main(string[] args)
{
var barracks = new Barracks();
Archer archer;
archer = barracks.ProduceArcher();
Console.WriteLine("new archer : {0}", archer.Characteristics());
barracks.Upgrade();
Console.WriteLine("Barracks upgraded to 17 century");
archer = barracks.ProduceArcher();
Console.WriteLine("new archer : {0}", archer.Characteristics());
/*
* new archer : I am a 16th century archer
* Barracks upgraded to 17 century
* new archer : I am a 17th century archer
*/
}