jeremyfeld / objc-petcast-001

PetCast

Instructions

1. Create a class called FISPet. FISPet has a method called makeASound that returns an NSString that reads "Pet me!" It also has a method called eatSomething that returns an NSString that reads "Nom nom nom."

2. Create a second class called FISDog. FISDog should be a subclass of FISPet. The FISDog class should override makeASound to return "Woof!" Also, FISDogs are able to assaultTheMailman. This method returns an NSString that reads "I got the mail! I got the mail!"

3. In your FISAppDelegate application:didFinishLaunchingWithOptions:, create an instance of FISDog. Then...

   • Confirm that it barks and can assault the mailman!
   • Cast it to an FISPet and confirm that, even though the variable is now an FISPet, its makeASound still goes "Woof."
   • Create an instance of FISPet. Cast it to be an FISDog, and make it go "Pet me!" Can you call assaultTheMailman on this fake dog? Will it compile? Will it run?
   • Now try to make your FISDog that was cast as an FISPet assault the mailman. What happens? How might you make the method call work? See the hint below for more information.

Hint

It is possible to cast in-line by putting parentheses around an object. For instance, assume we had a FISCar class and a FISPorsche subclass, and the FISPorsche object had a property called isTurboCharged. The following would work:

FISCar *newCar = [[FISPorsche alloc] init];
((FISPorsche *)newCar).isTurboCharged = YES;

So, what is happening above? First, we have intialized a FISPorsche, but it has been assigned to a variable of type FISCar. Then when it is time to set the isTurboCharged property, we have re-cast newCar to its original FISPorsche type, so the compiler will let us access its isTurboCharged property. Note the extra set of parentheses before .isTurboCharged.