1.AppDelegate.h and AppDelegate.m
When the application is created there are AppDelegate.h files and AppDelegate.m files by default. AppDelegateis a proxy for the whole application, it provides a monitoring interface to setting the program when it’s in the start, background, exit and active.
2.Class methods and instance methods
There are two types of methods in Objective-C: class methods and instance methods. Like “ - (void) setnumber: (int) n; “ that begin with symbol “-“ means that the
method is an instance methods. Instance methods are some of the operations performed on a particular instance of a class. For example, there is a white rabbit, it’s weight has increasted. We can define a instanse methods of weught to reflect the weight change of the white rabbit.
Class methods are some of the operations performed on the class itself. For example, we create a new calss, this method is class methods.
