Sending a notification when the operation has been completed in one class?

Question

I have two classes, Class A and Class B.

Class A has a method

 -(void)methodA:(id)sender
{

}

and Class B has a method

-(void)methodB:(id)sender
{

}

Now i have some work is happening in methodA ,So once it is completed i want to send a notification from methodA: to methodB: So i can do some operation on the basis of notification.

So how can i do this? Can anybody guide me as i am new to obj-c?