#import 
     
      // --------------------------------------------------@interface Tire : NSObject@end // Tire@implementation Tire- (NSString *) description{    return (@"I am a tire. I last a while");} // description@end // Tire// --------------------------------------------------@interface Engine : NSObject@end // Engine@implementation Engine- (NSString *) description{    return (@"I am an engine.  Vrooom!");} // description@end // Engine// --------------------------------------------------@interface Car : NSObject{    Engine *engine;    Tire *tires[4];}- (void) print;@end // Car@implementation Car- (id) init{    if (self = [super init]) {        engine = [Engine new];                tires[0] = [Tire new];        tires[1] = [Tire new];        tires[2] = [Tire new];        tires[3] = [Tire new];    }        return (self);    } // init- (void) print{    NSLog (@"%@", engine);        NSLog (@"%@", tires[0]);    NSLog (@"%@", tires[1]);    NSLog (@"%@", tires[2]);    NSLog (@"%@", tires[3]);    } // print@end // Car// --------------------------------------------------int main (int argc, const char * argv[]) {    Car *car;        car = [Car new];    [car print];        return (0);    } // main
     

运行结果:

I am an engine. Vrooom!

I am a tire. I last a while.

I am a tire. I last a while.

I am a tire. I last a while.

I am a tire. I last a while.