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design-patternsumlfacade
Jesper
Jesper

Reputation: 2094

Design Patterns - Understanding Facade Pattern

I'm new to Design Patterns and am trying to learn how they typically look like. Right now I'm trying to understand the Facade Pattern. I feel like the Facade Pattern is a rather broad concept, and so I was wondering if my second diagram would be considered a part of the Facade Template.

I know a typical Facade Pattern basically looks like this(with the A-class being the facade):

enter image description here

But what if we have a more subtle diagram like this:

enter image description here

Would the A-class still be considered a Facade-class or does it depend on the context?

Upvotes: 2

Views: 1498

Answers (4)

tebok
tebok

Reputation: 390

Of course, there's an exception when working with the compound design pattern but normally especially in your case, the facade class would not change. Also, new dependencies can be added at any time. Hope this helps.

Great Platform to learn Design Patterns

Upvotes: 0

Fuhrmanator
Fuhrmanator

Reputation: 12882

First, to understand facade, I like to think of it as a kind of refactoring. Imagine both your diagrams without the facade classes. The clients would have to interact directly with all the classes that the facade manages. As such, they would be more complex, with more coupling.

A facade provides a simplified service to the clients (reducing coupling), hiding the complexity behind the facade.

My favorite example (in Java) is the JOptionPane class. It did not exist in the earliest versions of Java, and if you wanted to create a Yes/No question dialog, you (as a client) had to manage all the calls to Dialog, Button, etc. as well as handle the events, etc. All that complexity has been simplified into a static method inside the JOptionPane facade class. Here's a UML diagram from https://best-practice-software-engineering.ifs.tuwien.ac.at/patterns/facade.html

enter image description here

Now to your question:

Would the A-class still be considered a Facade-class or does it depend on the context?

If A is providing a simplified service to the clients that effectively uses the complex subsystem of B, C, F and E, without which the clients would have to interact with (be coupled to) all of them directly, then I'd say A is a facade.

Upvotes: 3

jaco0646
jaco0646

Reputation: 17066

Yes, the A class is as much a Façade in the second example as in the first, insofar as A is the sole entry point between the clients and the "subsystem". Whether the hidden subsystem is flat or hierarchical is immaterial to the clients or indeed, to the pattern.

Do note that the perceived utility of a Façade is somewhat proportional to the complexity it abstracts (hides) from clients. So the first example may be considered a more useful Façade as it hides four additional classes. The second example only hides two classes from the clients, assuming they would interact only with B and C in the absence of A.

Upvotes: 0

dstar55
dstar55

Reputation: 954

I would say it depends of the context.

If you are new to Design Patterns, than real life stories which describes a design patterns, can help you to speed up with learning/understand the topic.

Upvotes: 0

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