Objective-C 关于super的问题

有三个类，Question,Choice,blank，其中Question是其他两个类的父类。
在Qestion中定义下面的方法:

- (instancetype)initWithQuestionType:(NSString *)questionType
{
    NSLog(@"**class:%@",[self class]);
    if([self isMemberOfClass:[Question class]])
    {
        self = nil;
        if([questionType isEqualToString:@"choice"])
        {
            NSLog(@"--class:%@",[self class]);
            self = [[Choice alloc] initWithQuestionType:questionType];
            NSLog(@"++class:%@",[self class]);
        }
        else
        {
            self = [[Blank alloc] initWithQuestionType:questionType];
        }

        return self;
    }

    return [super init];
}

- (instancetype)init
{
    NSLog(@"Init!");

    return [self initWithQuestionType:@"unknow"];
}

执行

 Question *question = [[Question alloc] initWithQuestionType:@"choice"];

输出是：

2015-10-16 20:58:50.278 initSample[3687:161396] **class:Question
2015-10-16 20:58:50.279 initSample[3687:161396] --class:(null)
2015-10-16 20:58:50.279 initSample[3687:161396] **class:Choice
2015-10-16 20:58:50.280 initSample[3687:161396] ++class:Choice

为什么没有输出init方法中的Init!这句话？

self = ［super init］