////  main.m#import 
     
      #import "Pet.h"#import "Person.h"#import "SuperMan.h"int main(int argc, const char * argv[]) {    @autoreleasepool {        Person *per = [[Person alloc]init];       [per test];       NSUInteger r = [per retainCount];        NSLog(@"%lu",r);        [per release];                        SuperMan *sm = [[SuperMan alloc]init];        Pet *pet = [[Pet alloc]init];        [sm setPet:pet];        [sm test];        [sm release];        [pet release];    }    return 0;}
     

////  Person.h#import 
     
      #import "Pet.h"@interface Person : NSObject{    Pet *_pet;//初始化}-(void)test;@end////  Person.m#import "Person.h"@implementation Person-(instancetype)init{    if (self=[super init]) {        self->_pet = [[Pet alloc]init];    }    return self;}-(void)test{    if (_pet) {        [_pet play];    }}-(void)dealloc{    NSLog(@"释放");    [_pet release];    [super dealloc];}@end
     

////  Pet.h//  关联对象的内存管理#import 
     
      @interface Pet : NSObject-(void)play;@end////  Pet.m//  关联对象的内存管理#import "Pet.h"@implementation Pet-(void)play{    NSLog(@"play");}-(void)dealloc{    NSLog(@"Pet  释放");      [super dealloc];}@end
     

////  SuperMan.h#import 
     
      #import "Pet.h"@interface SuperMan : NSObject{    Pet *_pet;}-(void)setPet:(Pet*)mypet;-(void)test;@end////  SuperMan.m#import "SuperMan.h"@implementation SuperMan-(void)setPet:(Pet*)mypet{    //_pet  = mypet;        if (_pet!=mypet) {        [_pet release];        _pet = [mypet retain];    }}-(void)test{    if (_pet) {        [_pet play];    }}-(void)dealloc{    NSLog(@"Super man 释放");    [_pet release];    [super dealloc];}@end