static void Main()
{
TrainSignal trainSignal = new TrainSignal();
new Car(trainSignal);
new Car(trainSignal);
new Car(trainSignal);
trainSignal.HereComesATrain();
}
public Car(TrainSignal trainSignal)
{
// We are observing the trainSignal
// When something happens, the trainSignal notifies us via the StopTheCar method
trainSignal.TrainIsComing += StopTheCar;
}