Mark Cade's Study Guide p. 87 Q3: Pattern for Additional Responsibility

[Darya Akbari]

Hi,

please view the following question from Mark Cade's SCEA Study Guide p.87:

Which pattern allows for addition of responsibilities?

A. Proxy

B. Fa�ade

C. Decorator

D. Strategy

E. Adapter

What's the correct answer? Please with a small explanation .

Regards,
Darya

[Tom Adams]

Out of the 5 patterns listed Decorator is the only one whose intent is to add responsibilities. This seems a bit confusing because the decorator does not change the interface of the class it is decorating...I guess it means it can add additional logic to an existing method.

Proxy - provides a surrogate or placeholder object to control access to the original object.

Facade - defines a higher-level interface that makes the subsystem easier to use.

Decorator - attaches additional responsibilities to an object dynamically to provide a flexible alternative to changing object functionality without using static inheritance.

Strategy - allows you to change the behavior of a class by plugging in different method implementations.

Adapter - Adapter pattern acts as an intermediary between two classes, converting the interface of one class so that it can be used with the other.

[Darya Akbari]

Hi Tom,

thanks for the pattern details. I agree with you concerning the confusion .

To me the Strategy pattern was the one that can add responsibilities. Because I really understand the question in a sense that how to add new behavior.

But from the wording of the answers I am a little bit afraid that one has to memorize the exact wording as provided in Mark Cade's SCEA study guide

Regards,
Darya

[Peer Reynders]

Originally posted by Darya Akbari:
To me the Strategy pattern was the one that can add responsibilities. Because I really understand the question in a sense that how to add new behavior.

But the Strategy pattern isn't about adding new behavior - its more about making aspects of behavior exchangable. GOF's pr�cis for Strategy is:

Strategy (315) Define a family of algorithms, encapsulate each one, and make them interchangable. Strategy lets the algorithm vary independently from clients that use it.

[Darya Akbari]

Hi Peer,

with behavior I mean a family of algorithms exactly as the GOF definition for Strategy Pattern.

Regards,
Darya

[Peer Reynders]

Originally posted by Darya Akbari:
with behavior I mean a family of algorithms.

I wasn't quibbling about that.

Imagine a pastry creme bag with shell, star, and leaf nibs (decorating tubes). You do not use the bag without nibs and you basically use the pastry cream bag in a similar fashion with each nib. However each nib produces a differently shaped stream of pastry cream - each nib represents a different Strategy.

You usually buy a KitchenAid/Cuisinart kitchen machine to mix batter and knead dough - thats its primary job. But you can get an attachment for it to grind meat/shaping sausage - that attachment is more like a Decorator. It would be a proper Decorator if you were shaping sausage and kneading dough at the same time (not very sanitary though).