1.isKindOfClass
[subClassObj isKindOfClass:superClass]; 返回YES
[subClassObj isKindOfClass:subClass]; 返回YES
2.isMemberOfClass
[subClassObj isKindOfClass:superClass]; 返回NO
[subClassObj isKindOfClass:subClass]; 返回YES
总之:1与2都是实例方法,2比1更为严格
3.isSubclassOfClass是类方法
[subClass isSubclassOfClass:superClass]; 返回YES
[subClass isSubclassOfClass:subClass]; 返回YES