C#

<code>interface IVehicle
{
    void Start();
}

class Car : IVehicle
{
    public Car() { }
    public void Start() { Console.WriteLine("starting Car..."); }
}

class Truck : IVehicle
{
    public Truck() { }
    public void Start() { Console.WriteLine("starting Truck..."); }
}

--test class--
void StartVehicle(IVehicle vehicle)
{
    vehicle.Start();
}

void Main()
{
    Car myCar = new Car();
    IVehicle vehicle = (IVehicle)myCar;

    Truck myTruck = new Truck();
    IVehicle vehicle2 = (IVehicle)myTruck;

    StartVehicle(vehicle);
    StartVehicle(vehicle2);

}</code>

class MyArray : System.Array
{
   public Object GetXXX(int myKey)
   {
      foreach (Object obj in this)
      {
         // Find your object.
      }
      return null; // Object not found.
   }
}