@interface Greeting : NSObject
+ (void)sayGoodby;
+ (void)sayGoodbyWithMessage:
    (NSString *)message;
@end

@implementation Greeting

//no default parameter values: the
//short form calls the full one
+ (void)sayGoodby {
    [self sayGoodbyWithMessage:@"Goodby!"];
}

+ (void)sayGoodbyWithMessage:
    (NSString *)message {
    NSLog(@"%@", message);
}
@end

[Greeting sayGoodby];
//printed "Goodby!"

[Greeting sayGoodbyWithMessage:@"Hi"];
//printed "Hi"