A paragraph about Delegation pattern in Objective-C

In most commonly used programming languages, delegation pattern operates based on conformation or even similarity of objects. In this case it is very similar to delegation pattern in Objective C in which it heavily relies on protocols. However, this pattern can never be as effective in other languages as it is in Objective C. The reasons behind this is that Objective C supports categories which allow methods to be added to existing classes without having to subclass them or having to have access to the source code. In addition, Objective C provides @optional notation when creating protocols. Therefore, not all the methods in protocols have to be implemented. This feature, plus the ability to check if an object (in this case the delegate) responds to a specific message (using respondsToSelector), make delegation pattern in Objective C very convenient and useful. In other languages, for instance in Java, all the methods in an Interface should be implemented. As a workaround for this, many Java interfaces come with an adapter class, which is a common approach for not requiring the user to implement a lot of empty methods. However, it limits inheritance and makes the design inflexible. Using delegation pattern in Objective C, the relationship between an object and other objects declared in it, can be bidirectional easily.