Objective-C - 组合

#import <Foundation/Foundation.h>


// --------------------------------------------------

@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.