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![Example of beautiful design
int arr[] = {1, 4, 9, 16, 25}; // some values
// find the first occurrence of 9 in the array
int * arr_pos = find(arr, arr + 4, 9);
std::cout<< “array pos = “<< arr_pos - arr << endl;
vector<int> int_vec;
for(int i = 1; i <= 5; i++)
int_vec.push_back(i*i);
vector<int>::iterator vec_pos = find (int_vec.begin(), int_vec.end(), 9);
std::cout<< “vector pos = “<< (vec_pos - int_vec.begin());](https://image.slidesharecdn.com/threewaystoapplydesignprinciplesinpractice-150421101613-conversion-gate02/75/Three-ways-to-apply-design-principles-in-practice-6-2048.jpg)
![Scenario
a) How do we treat files
and folders alike?
b) How can we handle
shortcuts?
File
+ GetName()
+ GetSize()
+ …
- name: String
- size: int
- type: FileType
- data: char[]
- …
Folder
+ GetName()
+ GetFiles()
+ GetFolders()
+ …
- name: String
- files[]: File
- folders[]: Folder](https://image.slidesharecdn.com/threewaystoapplydesignprinciplesinpractice-150421101613-conversion-gate02/75/Three-ways-to-apply-design-principles-in-practice-38-2048.jpg)
![How about this solution?
FileItem
+ GetName()
+ GetSize()
+ Add(FileItem)
+ Remove(FileItem)
Folder
+ GetFiles()
+ …
File
- files: FileItem
+ GetType()
+ GetContents()
+ …
- type: FileType
- data: char[]
Shortcut
+ GetLinkedFileItem()
+ …
- linkToFile: FileItem](https://image.slidesharecdn.com/threewaystoapplydesignprinciplesinpractice-150421101613-conversion-gate02/75/Three-ways-to-apply-design-principles-in-practice-39-2048.jpg)
Uploaded byGanesh Samarthyam
Three ways to apply design principles in practice
The document discusses how to apply design principles effectively in software development to improve design quality, highlighting the importance of architectural principles and solid principles. It presents real-world scenarios and design patterns, such as the strategy, bridge, and decorator patterns, to illustrate practical applications of these principles. Additionally, it emphasizes the role of refactoring and design analysis tools in enhancing software design by addressing 'bad smells' and enabling better understanding.
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Three ways to apply design principles in practice
- 1. Three Ways toApply Design Principles in Practice Ganesh Samarthyam Consultant, Trainer, and Author ganesh.samarthyam@gmail.com www.designsmells.com
- 2. Why care aboutdesign quality and design principles?
- 3. The city metaphor Source:http://indiatransportportal.com/wp-content/ uploads/2012/04/Traffic-congestion1.jpg “Cities grow, cities evolve, cities have parts that simply die while other parts flourish; each city has to be renewed in order to meet the needs of its populace… Software- intensive systems are like that. They grow, they evolve, sometimes they wither away, and sometimes they flourish…”
- 4. Messy city ofsoftware
- 5. “Applying design principlesis the key to creating high-quality software!” Architectural principles: Axis, symmetry, rhythm, datum, hierarchy, transformation
- 6. Example of beautifuldesign int arr[] = {1, 4, 9, 16, 25}; // some values // find the first occurrence of 9 in the array int * arr_pos = find(arr, arr + 4, 9); std::cout<< “array pos = “<< arr_pos - arr << endl; vector<int> int_vec; for(int i = 1; i <= 5; i++) int_vec.push_back(i*i); vector<int>::iterator vec_pos = find (int_vec.begin(), int_vec.end(), 9); std::cout<< “vector pos = “<< (vec_pos - int_vec.begin());
- 7. "The critical designtool for software development is a mind well educated in design principles" - Craig Larman
- 8. SOLID principles • There&should&never&be&more&than&one&reason&for&a&class&to& change&& Single'Responsibility' Principle'(SRP)' • So6ware&en88es&(classes,&modules,&func8ons,&etc.)&should& be&open&for&extension,&but&closed&for&modifica8on& Open'Closed'Principle' (OCP)' • Pointers&or&references&to&base&classes&must&be&able&to&use& objects&of&derived&classes&without&knowing&it& Liskov’s'Subs<tu<on' Principle'(LSP)' • Depend&on&abstrac8ons,¬&on&concre8ons& Dependency'Inversion' Principle'(DIP)' • Many&clientGspecific&interfaces&are&beHer&than&one& generalGpurpose&interface& Interface'Segrega<on' Principle'(ISP)'
- 9.
- 10. How to applyprinciples in practice? Abstraction Encapsulation Modularization Hierarchy Code How to bridge the gap?
- 11. Real scenario #1 Initialdesign
- 12. Real scenario #1 ❖How will you refactor such that: ❖ A specific DES, AES, TDES, … can be “plugged” at runtime? ❖ Reuse these algorithms in new contexts? ❖ Easily add support for new algorithms in Encryption? Next change: smelly design
- 13. Time to refactor! Threestrikes and you refactor Martin Fowler
- 14.
- 15. Potential solution #2? Algorithmsnot reusable!
- 16.
- 17. Can you identifythe pattern?
- 18. You’re right: ItsStrategy pattern!
- 19. Real scenario #2 Initialdesign
- 20. Real scenario #2 Howto add support for new content types and/or algorithms?
- 21. How about thissolution?
- 22. Can you identifythe pattern structure?
- 23. You’re right: ItsBridge pattern structure!
- 24. Wait, what principledid we apply?
- 25. Open Closed Principle(OCP) Bertrand Meyer Software entities should be open for extension, but closed for modification
- 26. Variation Encapsulation Principle(VEP) Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides Encapsulate the concept that varies
- 27. Fundamental principle: Encapsulation Theprinciple of encapsulation advocates separation of concerns and information hiding through techniques such as hiding implementation details of abstractions and hiding variations
- 28. Enabling techniques forencapsulation
- 29. Use “enabling techniques”to apply design principles in practice Key-takeaway #1
- 30. Supporting new requirements Reviseddesign with new requirements TextView + Draw() BorderedTextView + Draw() + DrawBorder() ScrollableTextView ScrollableBordered TextView - borderWidth + Draw() + ScrollTo() - ScrollPosition + Draw() + ScrollTo() + DrawBorder() - ScrollPosition - borderWidth
- 31. Real scenario ❖ Howwill you refactor such that: ❖ You don't have to “multiply- out” sub-types? (i.e., avoid “explosion of classes”) ❖ Add or remove responsibilities (e.g., scrolling) at runtime? Next change: smelly design
- 32. How about thissolution? VisualComponent + Draw() TextView + Draw() ScrollDecortor BorderDecorator + Draw() + ScrollTo() - ScrollPosition + Draw() + DrawBorder() - borderWidth Decorator + Draw() component->Draw() Decorator::Draw() DrawBorder() Decorator::Draw() ScrollTo() Source: “Design Patterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994
- 33. At runtime (objectdiagram) Source: “Design Patterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994
- 34. Can you identifythe pattern? VisualComponent + Draw() TextView + Draw() ScrollDecortor BorderDecorator + Draw() + ScrollTo() - ScrollPosition + Draw() + DrawBorder() - borderWidth Decorator + Draw() component->Draw() Decorator::Draw() DrawBorder() Decorator::Draw() ScrollTo() Source: “Design Patterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994
- 35. You’re right: ItsDecorator pattern! Source: “Design Patterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994
- 36. Identify pattern usedin this code LineNumberReader lnr = new LineNumberReader( new BufferedReader( new FileReader(“./test.c"))); String str = null; while((str = lnr.readLine()) != null) System.out.println(lnr.getLineNumber() + ": " + str);
- 37. Decorator pattern inReader
- 38. Scenario a) How dowe treat files and folders alike? b) How can we handle shortcuts? File + GetName() + GetSize() + … - name: String - size: int - type: FileType - data: char[] - … Folder + GetName() + GetFiles() + GetFolders() + … - name: String - files[]: File - folders[]: Folder
- 39. How about thissolution? FileItem + GetName() + GetSize() + Add(FileItem) + Remove(FileItem) Folder + GetFiles() + … File - files: FileItem + GetType() + GetContents() + … - type: FileType - data: char[] Shortcut + GetLinkedFileItem() + … - linkToFile: FileItem
- 40. Composite pattern Source: “DesignPatterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994
- 41. Enabling techniques forencapsulation
- 42. Refactor “bad smells”to apply design principles in practice Key-takeaway #2
- 43. Tool driven approachfor design quality
- 44.
- 45.
- 46.
- 47. Critique, code-clone detectors,and metric tools Infusion www.intooitus.com/products/infusion
- 48. Critique, code-clone detectors,and metric tools Designite www.designite-tools.com
- 49. Critique, code-clone detectors,and metric tools PMD Copy Paste Detector (CPD) http://pmd.sourceforge.net/pmd-4.3.0/cpd.html
- 50. Critique, code-clone detectors,and metric tools Understand https://scitools.com
- 51. Technical Debt quantification/visualizationtools Sonarqube http://www.sonarqube.org
- 52.
- 53. Use design analysistools to apply design principles in practice Key-takeaway #3
- 54. Key take-aways ❖ Theeeffective ways to apply design principles in practice: ❖ Use “enabling techniques” ❖ Refactoring “bad smells” ❖ Use design analysis tools
- 55. Principles and enablingtechniques
- 56. “Applying design principlesis the key to creating high-quality software!” Architectural principles: Axis, symmetry, rhythm, datum, hierarchy, transformation
- 57.