舉兩個例子 一個animal 類 ,一個它的子類 Money

** Animal 類**

@interface Animal : NSObject

@end


 @implementation Animal

- (instancetype)init
{
    self = [super init];
    if (self) {
        NSLog(@"init:%@",[self class]);
    }
    return self;
}

+ (void)initialize {
    
    [super initialize];
    NSLog(@"initialize_1_Class:%@",[self class]);
}

@end

** Monkey 類**

@interface Monkey : Animal

@end

 
@implementation Monkey

- (instancetype)init
{
    self = [super init];
    if (self) {
        NSLog(@"init:%@",[self class]);
    }
    return self;
}

+ (void)initialize {
    
    [super initialize];
    NSLog(@"initialize_2_Class:%@",[self class]);
}

@end

** 運行和 打印結果 **

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    Animal * animal1 = [[Animal alloc]init];
    
    Animal * animal2 = [[Animal alloc]init];
    
    Animal * animal3 = [[Animal alloc]init];
    
    Animal * animal4 = [[Animal alloc]init];
    
    
    Monkey * monkey1  = [[Monkey alloc]init];
    Monkey * monkey2  = [[Monkey alloc]init];
    Monkey * monkey3  = [[Monkey alloc]init];
    
}



2016-07-12 17:34:58.918 InitiazeAndLoad[5982:208086] initialize_1_Class:Animal
2016-07-12 17:34:58.918 InitiazeAndLoad[5982:208086] init:Animal
2016-07-12 17:34:58.918 InitiazeAndLoad[5982:208086] init:Animal
2016-07-12 17:34:58.918 InitiazeAndLoad[5982:208086] init:Animal
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] init:Animal
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] initialize_1_Class:Monkey
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] initialize_2_Class:Monkey
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] init:Monkey
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] init:Monkey
2016-07-12 17:34:58.919 InitiazeAndLoad[5982:208086] init:Monkey
2016-07-12 17:34:58.920 InitiazeAndLoad[5982:208086] init:Monkey
2016-07-12 17:34:58.920 InitiazeAndLoad[5982:208086] init:Monkey
2016-07-12 17:34:58.920 InitiazeAndLoad[5982:208086] init:Monkey

** 總結 **

1. initialize 在相同的類的時候只初始化一次，如果有繼承類，還會調(diào)用一次。2.我們應該只是初始化一些 固定的值