Objective-C Fundamentals

132 CHAPTER 6 Extending classes
applications. NSLog supports C-based placeholders such as %@ and %d. When the %@
placeholder is put in an NSString, the placeholder is filled with what is returned by this
method. You’ll implement this method in your three classes and see it work in an NSLog.
6.4.1 Overriding the description method
Overriding a method is done by simply declaring it in the class in which you would
like to call it. Start in the Person class, go into the Person.m file, and declare the
method shown here:
- (NSString *)description {
if (gender == Male) {
return [NSString stringWithFormat:
@"Hi! I am a man, named %@, who is %@ years old",
name, age];
} else {
return [NSString stringWithFormat:
@"Hi! I am a woman, named %@, who is a %@ years old",
name, age];
}
}
The description method is declared in NSObject. By placing the same method in your
class, you’re telling this class that rather than using the NSObject version of the
description method, you want this method to be called. Now you override the description
methods for both Teacher and Student, taking advantage of Person’s description
method in the ones you create in Student and Teacher so that you can write as little
code as possible:
- (NSString *)description {
if(gender == Male) {
return [NSString stringWithFormat:
@"%@. I am a male currently teaching %@ "
Figure 6.1 The compiler
checking the superclass