复合（Objective-C）

//实现CarParts
#import<Foundation/Foundation.h>


@interface Tire : NSObject
@end


@implementation Tire
-(NSString *)description
{
    return (@"I am a tire.I last a while.");
}
@end


@interface Engine : NSObject
@end


@implementation Engine
-(NSString *)description
{
    return(@"I am an engine.Vrooom!");
}
@end


@interface Car : NSObject
{
  Engine *engine;
  Tire *tires[4];
}
-(Engine *)engine;
-(void)setEngine:(Engine *)newEngine;
-(Tire *)tireAtIndex:(int)index;
-(void)setTire:(Tire *)tire atIndex:(int)index;
-(void)print;
@end


@implementation Car
-(Engine *)engine
{
    return(engine);
}
-(void)setEngine:(Engine *)newEngine
{
    engine=newEngine;
}
-(void)setTire:(Tire *)tire atIndex:(int)index
{
    if(index<0||index>3)
    {
        NSLog(@"bad index (%d) in setTire:atIndex:",index);
        exit(1);
    }
    tires[index]=tire;
}
-(Tire *)tireAtIndex:(int)index
{
    if(index<0||index>3)
    {
        NSLog(@"bad index (%d) in tireAtIndex:",index);
        exit(1);
    }
return (tires[index]);
}
-(void)print
{
    NSLog(@"%@",engine);
    NSLog(@"%@",tires[0]);
    NSLog(@"%@",tires[1]);
    NSLog(@"%@",tires[2]);
    NSLog(@"%@",tires[3]);
}
@end


int main(int argc, const char * argv[])
{


    Car *car=[Car new];
    Engine *engine=[Engine new];
    [car setEngine:engine];
    for(int i=0;i<4;i++)
        {
            Tire *tire=[Tire new];
            [car setTire:tire atIndex:i];
        }
    [car print];
    return 0;
}