Objective-C Fundamentals

126 CHAPTER 6 Extending classes
This is a very simple class that has instance variables (ivars) that all people share. Every
person has a name, age, and gender. Let’s subclass the Person class by making
Teacher and Student classes.
Click File > New File and create a new Objective-C Class called Teacher as a subclass
of Person, as shown in the following listing.
Listing 6.2
Creating the Teacher class
#import
#import "Person.h"
@interface Teacher: Person {
NSArray *classes;
NSNumber *salary;
NSString *areaOfExpertise;
}
- (id)initWithName:(NSString *)_name
age:(NSNumber *)_age
gender:(Gender)_gender
classes:(NSArray *)_classes
salary:(NSNumber *)_salary
areaOfExpertise:(NSString *)_areaOfExpertise;
@end
Next, click File > New File and create a new Objective-C Class called Student as a subclass
of Person, as shown in the following listing.
Listing 6.3
Creating the Student class
#import
#import "Person.h"
@interface Student: Person {
NSArray *classes;
NSNumber *numberOfCredits;
NSString *major;
}
- (id)initWithName:(NSString *)_name
age:(NSNumber *)_age
gender:(Gender)_gender
classes:(NSArray *)_classes
numberOfCredits:(NSNumber *)_numberOfCredits
major:(NSString *)_major;
@end
Now you’ve created your Teacher and Student classes as subclasses of Person. A
Teacher object now has a name, age, and gender, as defined in Person, but it is
extended by adding a list of classes, salary, and area of expertise. Similarly, a Student
has a name, age, and gender as well as a list of classes, a number of credits, and a
major. In this example, the superclass of both Teacher and Student is Person. The