oc 对象调用方法流程

isa & superclass

isa

• instance->isa & ISA_MASK = class
• class->isa & ISA_MASK = meta
• meta-isa & ISA_MASK = metarootclass

superclass

• class->superclass = superclass
• superclass->superclass = rootclass
• rootclass->superclass = nil

metarootclass->surperclass = Root class

@interface NSObject<NSObject>
- (void)test;
@end

@interface BNStudent : NSObject
@end
//会调用NSObject 的 -test方法
[BNStudent  test]