Understanding GOF Design Pattern With Simple Examples - Part One

Example

Consider we have a third party tool which does not have proper interface or code to fit into our application. To match it, we need to extend the third party code as a wrapper.

External WCF call without data validation

In one of my applications, we had to call an external WCF service, but before calling the WCF service, we had to manipulate some of the data and had to validate certain logic in the part of WCF call. In this case, we created a wrapper WCF service which does manipulation, validation, and calls the WCF service call.

The ADO.NET providers, eg System.Data.SqlClient.SqlConnection, System.Data.OleDb.OleDbConnection etc. Each provider is an adapter for its specific database.

Observer

It is the pattern which communicates to the subscribed objects when there is a change in the subject.

Example

Customers get notified by email, message in the mobile, hard copy of letter in postal address when the loan application is approved by the bank.

Different Alert Systems

Customers, Dealers, Agents get notified when there is a change in the price of the stock.

Parent Pages which are opened in a single page application get notified when there is a change in data in a pop up.

Events and delegates in the .net framework are examples of observer pattern.

Facade

When we design a system, we call different services, external service calls, database calls which altogether makes the system complex. Actually, exposing internal calls is not important to the clients. Only client needs to call some code that internally can communicate to the different systems or different services involved in it.

Façade design pattern is used when a system is very complex or difficult to understand how it is working internally.

Example

Different Bank ATM cards Working process in a single ATM Machine

When withdrawing money from an ATM we are not aware of how the transaction happens internally from the same bank or a different bank.

From the .net framework System.Xml.Serialization.XmlSerializer.XmlSerializer is an example of façade pattern. It hides a complex task converting objects into xml formats behind the scenes.

Template

The same business rule applies for the entire client with some variation. The method skeleton can be put in an abstract class and different client implementation can be put in the derived class.

Example

In a report generation module, customer requirement is to generate different type of reports either HTMLReport, PDF report , excel report or in a flat file report where the report header , logo and footer keep constant .

Master page in ASP.NET is an example of template pattern.

Chain of Responsibility

In this pattern we have chains of objects which keep on passing on different chains.

Loan or Leave approval process where a request passes between multiple stages. We apply for a loan it goes to validation, verification, approval process. In each process there should be a set of rules where they can approve a certain stage or pass the request chain to next immediate chain flow.

In any organization we see lot of projects, many variety of skill sets depending upon the customer projects.

In a MS.NET team different teams are there, but the base skill sets are ASP.NET, C#, SQL Server.

The new requirement 1 will keep on asking give me candidates with additional skill sets of WCF, WEB API as a top up skills

The new requirement 2 will keep on asking give me candidates with additional skill sets of WCF, ANGULAR JS as a top up skills

The new requirement 3 will keep on asking give me candidates with additional skill sets of WEB API, ANGULAR, WCF and ASP.NET MVC top up skills

On this example, the Base Skill set object gets appended to different skill sets dynamically, based on the project need.

Different stream classes in .NET framework Stream, MemoryStream, BufferedStream, FileStream are example of decorator pattern

Conclusion

I hope you got some information on GOF design pattern. Please put your comments or suggestions below .Thank you very much for reading this article.