Refactoring
Advanced Programming
SUT • Spring 2019
Refactoring
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.
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.
Refactoring
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By continuously improving the design of code, we make it easier and easier to work with
Joshua Kerievsky, Refactoring to Patterns
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
Bad Smell
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A bad smell in code
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Any symptom in the source code that possibly indicates a deeper problem.
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The term is coined by Kent Beck.
Bad Smells
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If it stinks, change it!
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Kent Beck and Martin Fowler.
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Bad smells in code
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Bad smells are source of problems
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Remove bad smells
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How?
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By Refactoring
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Bad Smells
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Duplicated Code
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Long Method
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Large Class
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Long Parameter List
-
…
Refactoring Techniques
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Extract Method
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Move
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Method
-
Variable
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Class
-
-
Extract Class
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Rename
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Method
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Variable
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Class
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Pull Up
-
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Push Down
IDE Support
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Refactoring techniques are widely supported by IDEs
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Practice it in Intelij
The Two Hats
- Kent Beck's metaphor of two hats
- Divide your time between two distinct activities
- adding function
- refactoring
Why Should I Refactor?
- Refactoring Improves the Design of Software
- Refactoring Makes Software Easier to Understand
- Refactoring Helps You Find Bugs
- Refactoring Helps You Program Faster
- Refactoring makes your code more maintainable
When Should You Refactor?
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The Rule of Three:
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Refactor When You Add Function
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Refactor When You Need to Fix a Bug
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Refactor As You Do a Code Review
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Example
public class Main {
public void main(String[] args){
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!
Example
public class Main {
public void main(String[] args){
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…
Example
public 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…
Example
public class Main {
public static void main(String[] args){
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");
}
}
Extract Class…
Example
public class Rectangle {
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 rectangle = new Rectangle(length, width);
return rectangle;
}
}
Extract Method…
Refactored Code
public class Main{
public static void main(String[] args){
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");
}
}
Final Refactor ...
References
- Refactoring: improving the design of existing code, Martin Fowler, Kent Beck, John Brant, William Opdyke, Don Roberts (1999)
Title Text
Refactoring
By Behnam Hatami
Refactoring
Refactoring / Advanced Programming Course @ SUT, Spring 2019
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