Foundation Inheritance Hierarchy
Remember that classes can have an inheritance relationship with other classes. Although we did not mention it specifically we have already seen classes in Foundation that are in an inheritance relationship. The two classes that I am talking about are NSObject and NSString. NSString inherits from NSObject. You might also say that NSString is a kind of NSObject. Because of this relationship, NSString has all the properties and methods it needs to be and do what an object is.