Objective-C Fundamentals

142 CHAPTER 6 Extending classes
type of lease will have a fixed time and a fixed amount, and it won’t recur. The header
of CTFixedLease is similar to that of CTLease but in this case has ivars: totalRental
and numberOfWeeks. Insert the code from the following listing into the header file.
Listing 6.15
CTFixedLease.h
#import "CTLease.h"
@interface CTFixedLease : CTLease {
float totalRental;
int numberOfWeeks;
}
@property(nonatomic) float totalRental;
@property(nonatomic) int numberOfWeeks;
+ (CTLease *)fixedTermLeaseWithPrice:(float)totalRental
forWeeks:(int)numberOfWeeks;
@end
The implementation of CTFixedLease is similar to that of CTPeriodicLease. You set
both instance variables for the class and return an autoreleased instance. You also
make sure the description method prints out both of your instance messages in the
description. Use the code in the following listing for the implementation of
CTFixedLease’s main file.
Listing 6.16
CTFixedLease.m
#import "CTFixedLease.h"
@implementation CTFixedLease
@synthesize totalRental, numberOfWeeks;
+ (CTLease *)fixedTermLeaseWithPrice:(float)totalRental
forWeeks:(int)numberOfWeeks {
}
CTFixedLease *lease = [CTFixedLease alloc];
lease.totalRental = totalRental;
lease.numberOfWeeks = numberOfWeeks;
return [lease autorelease];
- (NSString *)description {
return [NSString stringWithFormat:@"$%0.2f for %d weeks",
self.totalRental, self.numberOfWeeks];
}
@end
With this useful collection of classes in place, you can properly model the data for
your application as you continue to build it.