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In Java programming, we must have connected to a database to fetch some data. It is another example of Facade pattern in the programming world. Ensure that the coupling between the Facade and the subsystems is loose. Changes in the subsystem should not affect the Facade, and vice versa.
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These members access the subsystem on behalf of the facade user, hiding the implementation details. The Facade pattern is classified under the structural design patterns category because it simplifies the way we interact with complex systems. It doesn’t change the system itself but encapsulates it behind a Facade, thus making it easier to use. This is achieved by designing a higher-level interface that encapsulates and hides the system’s complexities.
Facade design pattern – real-world example in C#
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The following UML diagram illustrates the interaction of clients, facade, and sub-system classes according to the facade pattern. In summary, the Facade Design Pattern is valuable when dealing with complex systems, aiming for a simplified interface, promoting loose coupling, and providing abstraction and encapsulation. It is a good choice when we want to enhance the usability and maintainability of our software.
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What problems does the facade pattern address?
It also promotes decoupling the subsystem from its potentially many clients. On the other hand, if the Facade is the only access point for the subsystem, it will limit the features and flexibility that "power users" may need. The Facade design pattern is a pattern that provides a simplified interface to a complex system. You can use the Facade design pattern when a system is too complex or difficult to understand. A Facade Pattern says that just "just provide a unified and simplified interface to a set of interfaces in a subsystem, therefore it hides the complexities of the subsystem from the client". A facade does not encapsulate the subsystem classes or interfaces.
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Reduced Complexity for Clients:
Rather than interacting with each class directly, you can introduce a Facade class to encapsulate the whole subsystem. This Facade becomes the entry point to the subsystem and provides a simple interface, thus abstracting away the complexities. It provides a simplified and unified interface to the subsystem. The Facade delegates Client requests to appropriate objects within the Subsystem; the Client typically does not interact with them directly. Use this pattern to simplify the problem when there are multiple complex subsystems and interacting with them individually is really difficult/cumbersome. The Factory Method design pattern is a creational design pattern that uses factory methods to create objects.
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The web site may require only limited access to this business logic. For example, the web site may need to show whether an item for sale has reached a limited level of stock. The IsLowStock method of the facade class could return a Boolean value to indicate this.
The Nitty-Gritty of Facade Pattern
Suppose we have an application with set of interfaces to use MySql/Oracle database and to generate different types of reports, such as HTML report, PDF report etc. So we will have different set of interfaces to work with different types of database. Now a client application can use these interfaces to get the required database connection and generate reports. But when the complexity increases or the interface behavior names are confusing, client application will find it difficult to manage it.
In other words, it is a wrapper class used to hide the implementation details. However, the use of the facade design pattern has some disadvantages. Because of its central role, the implementation of a facade is a tedious and complicated task, especially if it has to be inserted into existing code.
Then, if everything is fine (i.e. if the Product is available in stock), you need to make the Payment. To do this, the Client needs to create an instance of the Payment class and need to call the MakePayment method. If Payment is successful, then we need to send the Invoice to the customer and to do so, the Client needs to create an instance of the Invoice class and call the SendInvoice method.
Then the operator, on behalf of a restaurant, gives the voice interface, which is a facade for you. So now, you can order a Burger, and you need not worry about the complexity of preparing a Burger, like what all operations they perform or the temperature they will cook. Let's understand the example of facade design pattern by the above UML diagram.
This structural code demonstrates the Facade pattern which provides a simplified and uniform interface to a large subsystem of classes. "The Facade Pattern provides a unified interface to a set ofinterfaces in a subsytem. Facade defines a higher level interface thatmakes the subsystem easier to use." The Facade pattern simplifies and hides the complexity of large code blocks or APIs, providing a cleaner, understandable and easy of use interface.
We can create any number of facades for a particular complex subsystem. Similarly, we can find a lot of more examples which hide lots of internal complexities and provide simple to use interface to the programmer to work with the system. While we have covered the Facade design pattern’s basics and applied it to some common scenarios, let’s explore its usage in more complex, real-world situations. We could create an ECommerceFacade class that wraps around these subsystems and provides simpler methods to interact with them. If clients are dependent on direct access to certain classes of the sub-system, this can also be granted in the facade pattern model. In this case, only the visibility of the sub-system needs to be programmed so that a client can bypass the facade if necessary.
A design pattern is a general reusable solution to a commonly occurring problem within a given context in software design. Thus, it provides a simplified and unified interface on top of a complex sub-system. Design patterns are useful as they solve recurring problems and in general simplify code.
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