bird.cs

public class Bird {
  public virtual void Fly() { Console.Write("Fly"); }
}
public class Eagle : Bird {
  public override void Fly() { Console.Write("Eagle Fly"); }
}
public class Duck : Bird {
  public override void Fly() { Console.Write("Duck Fly"); }
}
public class Penguin : Bird {
  public override void Fly() { throw new NoFlyException(); }
}

var birds = new List { new Bird(), new Eagle(), new Duck(), new Penguin() };
foreach(var bird in birds) bird.Fly(); 
// Tới pengiun thì lỗi vì cánh cụt quăng Exception