一、苹果官方API的解释是：
isKindOfClass：Returns a Boolean value that indicates whether the receiver is an instance of given class or an instance of any class that inherits from that class.
isMemberOfClass：Returns a Boolean value that indicates whether the receiver is an instance of a given class.
isSubclassOfClass：Returns a Boolean value that indicates whether the receiving class is a subclass of, or identical to, a given class.
二、它们的作用的区别：
isKindOfClass：判断对象是否为某类或者其派生类的实例（对象方法）；
isSubclassOfClass：判断对象是否为某类或者其派生类的实例（类方法）；
isMemberOfClass：判断对象是否为某个特定类的实例（对象方法）；
