Inheritance hierarchy
All objects inherit (either directly or indirectly) from NSObject:
Figure 20.3 Inheritance diagram of some classes you know
![Inheritance diagram of some classes you know](/api/v2/epubs/9780133491920/files/Inheritance/Inheritance.png)
NSObject has many methods but only one instance variable: the isa pointer. Every object’s isa pointer points at the class that created it. (Get it? When you have a BNRPerson instance, that object “is a” BNRPerson. When you have an NSString instance, that object “is a[n]” NSString.)
Figure 20.4 Every object knows which class created it
![Every object knows which class created it](/api/v2/epubs/9780133491920/files/Inheritance/isa.png)
When you send a message to an object, ...
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