$//$ Street is an abstract class

$//$ OneWayStreet and TwoWayStreet derive from Street

$//$ On a OneWayStreet, it is illegal to make a U turn

$//$ On a TwoWayStreet, a U Turn reverses the travelling direction

$//$ Main program creates two Street child objects $-$ one OneWay and one TwoWay

$//$ and demonstrates what happens when you make a U Turn

$//$ on a OneWayStreet and a TwoWayStreet