Objective-C Fundamentals

Adding new instance variables
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superclass of a class is the class that a new class is subclassing. Although this is the most
straightforward example of subclassing, you can subclass in many different ways, with
subtle distinctions between them.
6.2 Adding new instance variables
Now that your class files are created and their header files filled in, you can continue
to implement them. You need to start filling in the .m files for all the classes you created.
The .h file simply outlines what types of operations and variables a class uses.
The .m file is the piece of code that implements the creation of these variables and
the execution of the declared methods.
Any instance variable that your subclass has must be initialized. Right now, these
variables have types and names, but you must tell the application to allocate some
space in memory for them and to connect these variable names to actual memory.
This is usually done in two parts. First, the variable needs to have space allocated for it,
using the alloc method. Second, the variable must be initialized, using the init
method of your class. Every class should have an init method where the instance variables
and general setup for the class are performed. Let’s set up the init methods for
your new classes.
Go into the Person.m file. You’ll see an essentially blank class. You’ll make the initialization
method for this class so that you can use it in your project. Enter the code
from the following listing into Person.m.
Listing 6.4
Creating the init method for the Person class
#import "Person.h"
@implementation Person
- (id)init {
if ((self = [super init])) {
name = @"Person";
age = [NSNumber numberWithInt:-1];
gender = Male;
}
b
A blank initialization
method
}
return self;
- (id)initWithName:(NSString *)_name {
if ((self = [super init])) {
name = _name;
age = [NSNumber numberWithInt:-1];
gender = Male;
}
c
Method takes
name for person
}
return self;
- (id)initWithAge:(NSNumber *)_age {
if ((self = [super init])) {
d
Method takes
age for person