1. Advanced Programming in Java
Refactoring
Mehdi Einali

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
Programmer with overtime task: “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
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
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. Find bad smells! Refactor the Code!
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();
int b1 = s.nextInt();
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
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(); int width2 = scanner.nextInt(); 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) {
Extract Class…

21. Scanner scanner = new Scanner(System. in); System. out
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); width = scanner.nextInt(); 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
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. Make it hard for bugs to hide
Clean code does one thing well

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

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