Objective-C Fundamentals

134 CHAPTER 6 Extending classes
Person *person = [[Person alloc]
initWithName:@"Collin"
age:[NSNumber numberWithInt:23]
gender:Male];
Student *student = [[Student alloc]
initWithName:@"Collin”
age:[NSNumber numberWithInt:23]
gender:Male
classes:[NSArray arrayWithObjects:@"English",
@"Spanish",
@"Math", nil]
numberOfCredits:[NSNumber numberWithInt:12]
major:@"CS"];
Teacher *teacher = [[Teacher alloc]
initWithName:@"Winslow"
age:[NSNumber numberWithInt:30]
gender:Male
classes:[NSArray arrayWithObjects:@"ARM",
@"Imerssive Gaming",
@"Physical Computing", nil]
salary:[NSNumber numberWithInt:60000]
areaOfExpertise:@"HCI"];
}
NSLog(@"My person description is:\n%@", person);
NSLog(@"My student description is:\n%@", student);
NSLog(@"My teacher description is:\n%@", teacher);
Here you create Person, Teacher, and Student objects. At the end, you place a %@
placeholder in your NSLog input. When you pass an object in after the string, the %@ is
replaced with what is returned from each object’s description: method. With this
done, you’re going to look at another way to modify classes’ functionality behind the
scenes through a design method called clusters.
6.5 Class clusters
Class clusters is the Objective-C answer for the idea of abstraction. Generally, an abstract
superclass is declared with methods that are implemented in nonvisible, concrete subclasses.
This type of design is called an abstract factory design in Apple’s documentation. It
has the benefit of simplifying the complexity of public classes by revealing only the
methods declared in the abstract parent class. The abstract superclass is responsible for
providing methods that create instances of the private subclasses.
6.5.1 Why use class clusters
Class clusters is really just a fancy way of saying “secret subclassing.” They allow developers
to create a single doorway into multiple rooms. There are two common motivations
for taking this design approach:
1 Performance/Memory
This type of design allows a developer to make a single class that can represent
the creation point for multiple objects that have significantly different memory