using System;

namespace JmennyProstor
{

    class Program
    {
        public static void Main(string[] args)
        {
            Trida trida = new Trida("ahoj", new ImplementaceNecehoA());

            try
            {
                trida.VykonnaMetoda();
            }
            catch (InvalidOperationException e)
            {
                Console.WriteLine("Exception caught");
            }

            trida.Polozka = 1;
            trida.VykonnaMetoda();

            trida = new Trida(2, "nazdar", new ImplementaceNecehoB());
            trida.VykonnaMetoda();
        }
    }

    public interface Rozhrani
    {
        string Neco();
    }


    public class Trida
    {
        private Rozhrani necoService;

        public Trida() { }

        public Trida(string retezec, Rozhrani neco)
        {
            this.Retezec = retezec;
            this.necoService = neco;
        }

        public Trida(int polozka, string retezec, Rozhrani neco)
        {
            this.polozka = polozka;
            this.Retezec = retezec;
            this.necoService = neco;
        }

        public void Metoda()
        {
            return;
        }

        private int polozka;
        public int Polozka
        {
            get { return polozka; }
            set { if (value > 0) polozka = value; }
        }

        public string Retezec
        {
            get;
            private set;
        }

        public void VykonnaMetoda()
        {
            if (polozka == 0)
                throw new InvalidOperationException("Polozka is not properly set.");

            Console.WriteLine("Vykonavam ve stavu {0}, {1} za pomoci {2}", polozka, Retezec, necoService.Neco());
        }
    }

    public class Trida2 : Trida
    {
        public override void Metoda()
        {
            return;
        }
    }

    public class ImplementaceNecehoA : Rozhrani
    {
        public string Neco()
        {
            return "A";
        }
    }

    public class ImplementaceNecehoB : Rozhrani
    {
        public string Neco()
        {
            return "B";
        }
    }
}