Chapter 17 in brief


isa: NSObject has many methods, but only one instance variable, the isa pointer. Every object’s isa pointer points back to the class that created it. In order to respond a message, the object uses the isa pointer to find its class.
Overriding methods: You can override a method with a custom implementation. This implementation is so easy and you can override a method by defining a method in an object in a way that you want but remember that the arguments and method’s name is same as original method and the only thing that is different is the body of method.
How to advertise a method? Declaring a method in the header file advertises the method so that instances of other classes can call it.
Super: The super directive says “Run this method, but start the search for its implementation at my superclass”. It uses when you want to override a method.