- (NSString *)description

{

    return @"description 来自对象描述";

}

+ (NSString *) description

{

    return @"description 来自类描述";

}

CTPerson *person =  [[CTPerson alloc] init];

NSLog(@"%@",person);  //输出"description 来自对象描述"

NSLog(@"%@",[CTPerson class]); //输出"description 来自类描述"