This document discusses refactoring software by restructuring code without changing its observable behavior. It provides examples of factors in algebra and how software is composed of components like methods, objects, and classes. Refactoring helps improve software design, find bugs, and change software to adapt to new requirements while preserving functionality. Common refactorings include extracting methods and classes, replacing magic numbers, and moving code. Design patterns like Proxy, Singleton, and State are also discussed as approaches to solving recurring problems.

1. Refactoring et al
Naveen Muguda

2. Factors
Factors are numbers you can multiply together to get another number:
Example: 2 and 3 are factors of 6, because 2 × 3 = 6.
3 and 4 are factors of 12, because 3 × 4 = 12.
Also 2 × 6 = 12 so 2 and 6 are also factors of 12.
In Algebra, factors are what you can multiply together to get an expression.
(x+3) and (x+1) are factors of x2
+ 4x + 3:

3. Software,Composition
Software is composed by combination of
components
components can be
● methods
● objects
● functions
● classes

4. Refactoring
to restructure software without changing its
observable behavior.
change from 2*6 to 3*4, while the product
remains 12

5. Why?
Understand your code better
4398046511104 => 2 ^ 42

6. Why?
Improve your design of your software
21600 = 2^5 * 3 ^ 3 * 5 ^ 2

7. why?
find bugs
reasoning about factors helps you to find bugs
is a number power of 2?
!(x & (x - 1))

8. refactoring in the real world
Refactor (verb): to restructure software by
applying a series of refactorings with-
out changing its observable behavior.

9. refactoring in Test Driven Design
red green refactor

10. Change
need to Change doesn’t change
● business evolves
● rules change
● new users, new use cases
● more data
● …..

11. Two Hats
Software Development has two distinct
activities
1. adding functionality
2. refactoring

12. Two Hats: Metaphor
(x + 1) (x + 3) + 2 x^2 + 3x - 1
=> 3 x^2 + 7x + 2
=> (3x + 1) (x + 2)

13. Two hats ...
swap hats frequently.
add new functionality,
realize this would be much easier if the code
were structured differently.
refactor for a while.

15. Bad Smells
● Wrong Name
● Long Method
● Large Class
● Long Parameter List

16. Bad Smells
● Duplicated code
● Switch statement

17. ...
● Divergent Change
● Shotgun Surgery

18. Refactorings
● extract method
● Introduce Explaining Variable
● Split Temporary Variable
● Remove Assignments to Parameters
● Replace Magic Number with Symbolic
Constant

19. ...
● Move Method
● Extract Class
● Move Field

20. ...
● encapsulate field
● encapsulate collections

22. Design Patterns
Some problems keep re-appearing
providing a name increases design vocabulary
raises level of abstraction
easier for communication
problem/solution gets well understood

23. Proxy
Provides a place holder for another object
applications
● remote proxy
● protection proxy
● smart proxy

25. Singleton
● restricts instantiation to only one object
● mechanism to access this object without
creating it
● class level method to retrieve this object
● constructor made private

26. State
allows objects to change behavior when its
internal state changes
Participants
● State
● Concrete State Subclasses