Refactoring Mehdi Einali Advanced Programming in Java 1

2 Tale of Messy code

3 Once upon a time … A team start a project Project got many attention and team has to add new features in short time “I will fix this later”

4 After a while Changes slowed down by messy code As productivity decreases more programmer assigned to project New programmer with messy code results in more messy code

5 rebellion Eventually the team rebels. A new tiger team is selected Best technologies has been chosen Now the two teams are in a race This race can go on for a very long time Tiger team is now under pleasure of comparison with old low feature but working version once upon a time Messy code again and again once upon a time

6 refactoring

7 Refactoring A disciplined way to restructure code in order to improve code quality without changing its behavior A change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior.

8 Refactoring Refactoring is the process of changing a software system In such a way that it does not alter the external behavior of the code But improves its internal structure It is a disciplined way to clean up code It minimizes the chances of introducing bugs When you refactor, you are improving the design of the code after it has been written.

9 Refactoring By continuously improving the design of code, we make it easier and easier to work with Joshua Kerievsky, Refactoring to Patterns

10 Example Duplicate Code What are the drawbacks? What is the solution? Refactoring: Finding a “Bad Smell” Changing the code to remove the bad smell Some well-known bad smells are reported

11 Bad Smell A bad smell in code Any symptom in the source code that possibly indicates a deeper problem. The term is coined by Kent Beck.

12 Bad Smells Duplicated Code Long Method Large Class Long Parameter List Divergent Change …

13 Refactoring Techniques Extract Method Move Method Variable Class Extract Class Rename Method Variable Class Pull Up Push Down

14 IDE Support Refactoring techniques are widely supported by IDEs

15 The Two Hats Kent Beck's metaphor of two hats Divide your time between two distinct activities adding function refactoring

16 Why Should I Refactor? Improves the Design of Software Makes Software Easier to Understand Helps You Find Bugs Helps You Program Faster Refactoring makes your code more maintainable

17 When Should You Refactor? The Rule of Three: Refactor When You Add Function Refactor When You Need to Fix a Bug Refactor As You Do a Code Review

18 Scanner s = new Scanner(System.in); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); int a1 = s.nextInt(); System.out.print("Enter the length: "); int a2 = s.nextInt(); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); int b1 = s.nextInt(); System.out.print("Enter the length: "); int b2 = s.nextInt(); int x = a1*a2; int y = b1*b2; if(x == y) System.out.println("Equal"); Find bad smells! Refactor the Code!

19 Scanner scanner = new Scanner(System.in); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); int width1 = scanner.nextInt(); System.out.print("Enter the length: "); int length1 = scanner.nextInt(); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); int width2 = scanner.nextInt(); System.out.print("Enter the length: "); int length2 = scanner.nextInt(); int area1 = width1*length1; int area2 = width2*length2; if(area1 == area2) System.out.println("Equal"); Rename…

20 class Rectangle{ private int length, width; public int getLength() { return length; } public void setLength(int length) { this.length = length; } public int getWidth() { return width; } public void setWidth(int width) { this.width = width; } public Rectangle(int length, int width) { this.length = length; this.width = width; } Extract Class…

21 Scanner scanner = new Scanner(System.in); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); int width = scanner.nextInt(); System.out.print("Enter the length: "); int length = scanner.nextInt(); Rectangle rectangle1 = new Rectangle(length, width); System.out.println("Rectangle Info."); System.out.print("Enter the width: "); width = scanner.nextInt(); System.out.print("Enter the length: "); length = scanner.nextInt(); Rectangle rectangle2 = new Rectangle(length, width); int area1 = rectangle1.getWidth()*rectangle1.getLength(); int area2 = rectangle2.getWidth()*rectangle2.getLength(); if(area1 == area2) System.out.println("Equal");

22 class Rectangle{... public int area(){ return length * width; } … int area1 = rectangle1.area(); int area2 = rectangle2.area(); Extract Method…

23 private static Rectangle readRectangle(Scanner scanner) { int width; int length; System.out.println("Rectangle Info."); System.out.print("Enter the width: "); width = scanner.nextInt(); System.out.print("Enter the length: "); length = scanner.nextInt(); Rectangle rectangle2 = new Rectangle(length, width); return rectangle2; } Extract Method…

24 Refactored Code Scanner scanner = new Scanner(System.in); Rectangle rectangle1 = readRectangle(scanner); Rectangle rectangle2 = readRectangle(scanner); int area1 = rectangle1.area(); int area2 = rectangle2.area(); if(area1 == area2) System.out.println("Equal");

25 Clean code

26 Clean code does one thing well Make if hard for bugs to hide

27 Reads like well-written prose Never obscure the designer’s intent

28 Provides one way rather than many ways for doing one thing

29 Each routine you read turn out to be pretty much what you expect

30 (Conclusion) Clean code is Make if hard for bugs to hide Clean code does one thing well Reads like well-written prose Never obscure the designer’s intent Provides one way rather than many ways for doing one thing Each routine you read turn out to be pretty much what you expect

31 notes Clean Programming is some thing like martial art Combination of technique and art. The Art of Computer Programming by Knuth Have different school of thoughts Clean Programming is skill Good learning results in good use forever Changing bad learning is hard Like Driving!

32 Reference Refactoring: improving the design of existing code, Martin Fowler, Kent Beck,John Brant, William Opdyke, Don Roberts (1999) Clean code,A handbook of agile software craftmanship,Robert C Martin,2008, Prentice Hall

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