Design patterns Structural
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The document discusses design patterns, defining them as solutions to recurrent problems, and highlights their components such as name, purpose, and constraints. It outlines the importance of studying design patterns for improving code maintainability, team communication, and object-oriented principles, as well as providing examples from a bookstore app and olx.com.pk. Different types of design patterns are categorized into structural, creational, and behavioral, with detailed explanations of specific patterns like adapter, bridge, and composite.
Design patterns Structural
- 1. Design Pattern Group Members: Mian Muhammad Abdullah SP16-BCS-217 Muhammad Umar SP16-BCS-212 Muhammad Danish SP16-BCS-196
- 2. Design Pattern? • Christopher Alexander defined a pattern as “a solution to a problem in a context” • “Each pattern describes a problem which occurs over and over again in our environment and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.”
- 3. Components Of Design Pattern • Name • Purpose • Way to accomplish and solve problem • Constraints
- 4. Why study Design Patterns? Because design patterns- • Help reuse existing high quality solutions to commonly occurring problems • Improve individual and team learning • Shift level of thinking to a high perspective • Illustrate basic object-oriented principles • Improves modifiability and maintainability of the code • Improve team communication and individual learning
- 5. Book Store App Design Pattern • Problem 1 Use of search Bar and Filter in App: Sometimes user have problem while Searching from search bar in order to resolve this problem we will define filter option and vice versa.
- 6. • Problem 2 There is problem occur when user Search wrong keyword but his/her Required book is available in data base In order to solve this problem we Some pre define options: • Use filter option • Pop up open for wrong entry • Guide use to enter correct keyword
- 7. • Problem 3 Problem 3 is most Important problem that is ignore by some brand website that is: Allowing publisher to write content according to his/her Experience. This problem de-rank app in google search because google ranking depends on % of optimized content. In order to solve this issue we follow some pre define rules and guide publisher about content while writing title, description and author detail of Book. From this design pattern our content is well managed and easily rank on google.
- 10. Structural design patterns • These design patterns are all about Class and Object composition. Structural class-creation patterns use inheritance to compose interfaces. Structural object-patterns define ways to compose objects to obtain new functionality.
- 11. Examples Adapter Match interfaces of different classes Bridge Separates an object’s interface from its implementation Composite A tree structure of simple and composite objects Decorator Add responsibilities to objects dynamically Facade A single class that represents an entire subsystem Flyweight A fine-grained instance used for efficient sharing Private Class Data Restricts accessor/mutator access Proxy An object representing another object
- 12. Adapter Design Pattern Match interfaces of different classes • In software engineering, the adapter pattern is a software design pattern that allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code. • Intent • Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. • Wrap an existing class with a new interface.
- 13. Bridge Design Pattern Separates an object’s interface from its implementation • Decouple an abstraction from its implementation so that the two can vary independently • Use the Bridge pattern when: – you want run-time binding of the implementation – you want to share an implementation among multiple objects
- 14. Composite Design Pattern A tree structure of simple and composite objects • Compose objects into tree structures to represent whole-part hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly • Use this pattern whenever you have "composites that contain components, each of which could be a composite".
- 15. Decorator Add responsibilities to objects dynamically • Attach additional responsibilities to an object dynamically • Decorators provide a flexible alternative to sub- classing for extending functionality
- 16. Façade A single class that represents an entire subsystem • Provide a unified interface to a set of interfaces in a subsystem • Facade defines a higher-level interface that makes the subsystem easier to use • Create a class that is the interface to the subsystem • Clients interface with the Facade class to deal with the subsystem • It hides the implementation of the subsystem from clients • It promotes weak coupling between the subsystems and its clients • It does not prevent clients from using subsystems class, should it?
- 17. Flyweight A fine-grained instance used for efficient sharing • Use sharing to support large numbers of fine- grained objects efficiently • The pattern can be used when: – The program uses a large number of objects and – The program does not use object identity (==)
- 18. Proxy An object representing another object • Provide a surrogate or placeholder for another object to control access to it. • The proxy has the same interface as the original object • Virtual Proxy: – Creates/accesses expensive objects on demand – You may wish to delay creating an expensive object until it is really accessed – It may be too expensive to keep entire state of the object in memory at one time
- 19. Benefits of Design Patterns Design patterns enable large-scale reuse of software architectures and also help document systems Patterns help improve developer communication. Pattern names form a common vocabulary Patterns help ease the transition to Object Oriented technology
- 20. Drawbacks of Design Patterns Patterns do not lead to direct code reuse Patterns are deceptively simple. Teams may suffer from pattern overload Patterns are validated by experience and discussion rather than by automated testing Integrating patterns is a human-intensive activity.
- 21. Suggestions for Effective Use Do not recast everything as a pattern Do not recast Instead, develop strategic domain patterns and reuse existing tactical patternsDevelop Clearly document when patterns apply and do not applyDocument Directly involve pattern authors with application developers and domain experts.Involve