Design Patterns : Solution to Software Design Problems
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The document outlines various software design patterns and their importance in creating efficient and flexible applications, highlighting the need for structured design to accommodate future changes. Key design patterns discussed include Chain of Responsibility, Mediator, and Observer patterns, with examples of their implementation. The content emphasizes that understanding design patterns is essential for software engineers to improve communication and problem-solving in software development.
Design Patterns : Solution to Software Design Problems
- 1. www.edureka.co/design-patterns View Design Patterns course details at www.edureka.co/design-patterns For Queries: Post on Twitter @edurekaIN: #askEdureka Post on Facebook /edurekaIN For more details please contact us: US : 1800 275 9730 (toll free) INDIA : +91 88808 62004 Email us : webinars@edureka.co Design Patterns : Solution to Software Design Problems
- 2. Slide 2 www.edureka.co/design-patterns At the end of this session, you will be able to: Objectives Know what are Software Design Patterns Understand the need of Software Design Patterns Distribute Responsibility using Chain Of Responsibility Pattern Communicate among objects with Mediator Pattern Understand Observer Patterns
- 3. Slide 3 www.edureka.co/design-patterns Software Design Patterns & Gang Of Four(GOF) Software design patterns describe relationship among classes to solve a general and repeatable design problem in a specific context with proven solution Anyone who knows something about Software Design Patterns will certainly be aware of famous book “Elements of Reusable Object-Oriented Software” written by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides popularly knows as Gang Of Four(GOF) This is the most popular book written on Software Design Patterns by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, known as Gang Of Four
- 4. Slide 4 www.edureka.co/design-patterns Classification of Software Design Patterns Software Design Patterns Creational Design Pattern Factory Pattern Object Pool Pattern Singleton Pattern Structural Design Pattern Adapter Pattern Decorator Pattern Composite Pattern Behavioral Design Pattern Chain of Responsibility Pattern Mediator Pattern ObserverPattern Concurrency Design Pattern Reactor Pattern Scheduler Pattern Thread Pool Pattern . . . . . . . . . . . .
- 5. Slide 5 www.edureka.co/design-patterns Importance of Design Patterns Just knowing a Programming Language is not enough to engineer a software application While building an application its important that we keep the future requirements and changes in mind otherwise you will have to change the code that you had written earlier Building a large application is never easy, so its very important that you design it correctly and then start coding the application Design Patterns provides efficient techniques to create a flexible application design
- 6. Slide 6Slide 6Slide 6 www.edureka.co/design-patterns Chain Of Responsibility pattern gives more than one object a chance to handle the request Sender of the request does not know which object in the chain will serve its request In Chain Of Responsibility pattern a chain of request handlers is maintained, a handler decides whether it can handle the request or not, if not then it passes the request to next handler Chain of Responsibility (COR) Receiver 1 Receiver 2 Receiver 3 Request Request Request Receiver N Request Reference to Receiver 2 Reference to Receiver 3 Chain of Receiver Reference to Receiver 4 Cannot handle
- 7. Slide 7Slide 7Slide 7 www.edureka.co/design-patterns 1. Handler - defines an interface for handling requests 2. ConcreteHandler - handles the requests it is responsible for .If it can handle the request it does so, otherwise it sends the request to its successor 3. Client - sends commands to the first object in the chain that may handle the command Handler +HandleRequest() ConcreteHandler1 +HandleRequest() ConcreteHandler2 +HandleRequest() Client Chain of Responsibility - UML Diagram
- 8. Slide 8Slide 8Slide 8 www.edureka.co/design-patterns Problem Statement Customer support system is one of the implementation of this pattern, where users calls the help desk (L1 support) and tell their problem L1 Support L2 Support Cannot handle Problem Statement Resolved Resolved YES NO YES NO Request goes through multiple objects (handlers)
- 9. Slide 9Slide 9Slide 9 www.edureka.co/design-patterns Solution Using Chain of responsibility simplifies the request object because it does not have to know the chain’s structure and keep direct references to its members In this case, user simply interact with help desk and the request internally goes through multiple handlers User does not need to know about the different handlers
- 10. Slide 10Slide 10Slide 10 www.edureka.co/design-patterns Implementing Chain of Responsibility Client (user) will generate a SupportRequest (a ticket) All support levels will have to inherit the support class and implement the handleRequest()
- 11. Slide 11Slide 11Slide 11 www.edureka.co/design-patterns Implementing Chain of Responsibility (Contd.)
- 12. Slide 12Slide 12Slide 12 www.edureka.co/design-patterns Implementing Chain of Responsibility (Contd.)
- 13. Slide 13Slide 13Slide 13 www.edureka.co/design-patterns Implementing Chain of Responsibility (Contd.) Here we are creating chain of responsible objects for handling the support request according to user query All the support requests will first go to L1 support Output
- 14. Slide 14Slide 14Slide 14 www.edureka.co/design-patterns Other Uses Of Chain of Responsibility One of the most important use of Chain Of Responsibility pattern is to implement filter mechanism Here one filter process the request and then passes on to next filter in the chain, similarly next filter processes the request and then passes onto next filter in chain JavaEE API uses Chain Of Responsibility pattern to implement filter mechanism using the following doFilter() method javax.servlet.Filter#doFilter(ServletRequest request, ServletResponse response, FilterChain chain) Request Logging Filter Authentication Filter Servlet JAX-WS also uses Chain Of Responsibility pattern to implement JWS Handler Framework, which allows manipulation of SOAP messages
- 15. Slide 15Slide 15Slide 15 www.edureka.co/design-patterns Mediator Pattern The mediator pattern promotes loose coupling of objects by removing the need for classes to communicate with each other directly Instead, mediator objects are used to encapsulate and centralize the interactions between classes Mediator pattern simplifies communication in general when a program contains large number of classes that interact Each class only needs to know how to pass messages to its mediator, rather than to numerous colleagues
- 16. Slide 16Slide 16Slide 16 www.edureka.co/design-patterns Mediator Pattern – UML Diagram Mediator - defines an interface for communicating with Colleague objects ConcreteMediator - knows the colleague classes and keep a reference to the colleague objects Colleague classes - keep a reference to its Mediator object Mediator ConcreteMediator ConcreteColleagueA ConcreteColleagueB Colleague
- 17. Slide 17Slide 17Slide 17 www.edureka.co/design-patterns Problem Statement Suppose you have to create a chat application where multiple users can chat together Rather than each user sending the message directly to other users, we can use mediator pattern to implement this design
- 18. Slide 18Slide 18Slide 18 www.edureka.co/design-patterns Implementing Mediator Pattern ChatMediator keeps the reference of all the users
- 19. Slide 19Slide 19Slide 19 www.edureka.co/design-patterns Implementing Mediator Pattern (Contd.) A User doesn’t have any reference to other users
- 20. Slide 20Slide 20Slide 20 www.edureka.co/design-patterns Output Implementing Mediator Pattern (Contd.)
- 21. Slide 21Slide 21Slide 21 www.edureka.co/design-patterns ContactSelectorPanel ContactDisplayPanel ContactEditorPanel 1. All GUI applications consists of small components like Windows, Panel etc. 2. Each Panel contains a group of GUI element 3. These panels have to co-ordinate among themselves 4. As in this application, whenever a contact is selected from the drop down box, its details should be updated in the ContactDisplayPanel and ContactEditorPanel 5. Rather then one panel having reference of all other panels, we can use Mediator Pattern to simplify the communication between panel objects Implementing Mediator Pattern (Contd.)
- 22. Slide 22 www.edureka.co/design-patterns Observer Pattern Observer SubjectObserves notify Observer: There is someone watching you
- 23. Slide 23 www.edureka.co/design-patterns Reference : tutorialspoint.com Observer Pattern
- 24. Slide 24 www.edureka.co/design-patterns Conclusion Similarly there are other design patterns to solve majority of the problems that software designers encounter during their day to day activities Design patterns compliments ones experience and helps them deliver wonderful and successful software designs They serve as common nomenclature or jargon that architects can easily communicate with others in software industry Software design is no more an art. It’s a skill one can learn. And thanks to design patterns