Refactoring Mehdi Einali Advanced Programming in Java 1.

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Refactoring

Mehdi Einali

Advanced Programming in Java

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Tale of Messy code

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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”

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After a whileChanges slowed down by messy code

As productivity decreases more programmer assigned to project

New programmer with messy code results in more messy code

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rebellionEventually the team rebels.

A new tiger team is selectedBest 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

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refactoring

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RefactoringA disciplined way to restructure code

in order to improve code qualitywithout 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.

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RefactoringRefactoring 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 structureIt is a disciplined way to clean up code It minimizes the chances of introducing bugsWhen you refactor, you are improving the design of the code after it has been written.

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Refactoring

By continuously improving the design of code, we make it easier and easier to work with

Joshua Kerievsky, Refactoring to Patterns

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ExampleDuplicate CodeWhat 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

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Bad SmellA bad smell in codeAny symptom in the source code that possibly indicates a deeper problem.The term is coined by Kent Beck.

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Bad SmellsDuplicated CodeLong MethodLarge ClassLong Parameter ListDivergent Change…

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Refactoring TechniquesExtract MethodMove

MethodVariableClass

Extract ClassRename

MethodVariableClass

Pull UpPush Down

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IDE SupportRefactoring techniques are widely supported by IDEs

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The Two HatsKent Beck's metaphor of two hatsDivide your time between two distinct activities

adding functionrefactoring

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Why Should I Refactor?Improves the Design of SoftwareMakes Software Easier to UnderstandHelps You Find BugsHelps You Program Faster

Refactoring makes your code more maintainable

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When Should You Refactor?

The Rule of Three:Refactor When You Add FunctionRefactor When You Need to Fix a BugRefactor As You Do a Code Review

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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!

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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…

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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…

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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");

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class Rectangle{...public int area(){

return length * width;}

}

…int area1 = rectangle1.area();int area2 = rectangle2.area();

Extract Method…

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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…

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Refactored CodeScanner 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");

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Clean code

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Clean code does one thing well

Make if hard for bugs to hide

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Reads like well-written prose

Never obscure the designer’s intent

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Provides one way rather than many ways for doing one thing

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

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(Conclusion)Clean code isMake if hard for bugs to hideClean code does one thing wellReads like well-written prose

Never obscure the designer’s intentProvides one way rather than many ways for doing one thingEach routine you read turn out to be pretty much what you expect

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notesClean 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 hardLike Driving!

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ReferenceRefactoring: 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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