In our quest against increasing complexity, Extract Method is probably the most important refactoring technique in our hands. We use it a dozen times per day as a first-level weapon, and very often it leads to us to deeper design insights. Let’s look at several such further actions you might take after pulling some code out in a separate method: * Reorder Parameters * Remove parameters by including more lines in what you extract (Ctrl-Z) * Add parameters for reuse by extract/inline variable at call site (Ctrl-Z) * Move method to object (for Feature Envy) * Encapsulate conditionals (great with Java8) * Inline back * Distill switch expressions: the 3 Clean Switch Rules * Introduce Method Object for heavy logic * Early return errors * Extract static util functions * Spawn smart Value Object vs logic in Utils * Extract’n-test then mock away, leading to Separation by Layers of Abstraction * Command-Query Separation: mind the side effects * Extract again - boolean vs SRP * Wrap call to safely add more code (Open-Closed)

1. Refactoring Games
15 things to do after Extract Method
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3. Victor Rentea
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6. 125

8. When you cannot find a satisfying name for a variable or a method,
choose a Welsh one.
You won't forget to change it later
- Mario Fusco

9. Rename
&
Extract Method

10. VictorRentea.ro
Extract Method
Selection
to Extract
variable
expression
Extract Variables
to generify/reuse
… then extract method
…then inline var back
Expand Selection
for less parameters

11. VictorRentea.ro
3. Ctrl-
2. Revert
1. Reader
Powers in Universe

12. Do you love switches?

13. VictorRentea.ro
A Clean Switch:
is the only instruction in a method
default: throw new
One-line per case
: return func();
: func(); break;
return switch
JEP 325: Switch Expressions
In Java 13… soon…

14. VictorRentea.ro
if (αααααα && βββββββ || γγγγγγγγ || ! δδδδδδδ)
Encapsulate Conditionals
if (α(..) && β(..) || γ(..) || ! δ(..))
if (αβ(..) || γδ(..))

16. VictorRentea.ro
Feature Envy
method(α, …)
α.method(…)
“Move” refactor
“Keep Behavior next to State”[OOP]

17. VictorRentea.ro
Discover Value Objects
privateMethod(α, β)
SomeUtil.publicHelper(α, β)
VO vo = new VO(α, β);
vo.method();
General-purpose? Never mocked?

18. Always Strive To
Deepen
your Domain Language

19. VictorRentea.ro
How to refactor God Methods
of 500 lines ?
Extract Method Object refactor
138
Hint
A class should have less
than 200-300 lines
You make it a class

20. VictorRentea.ro
No side effects
Prefer returning over changing
Pure Functions
139
Same result for same inputs
no externals, time or Random
convertUser(user):UserDto

22. VictorRentea.ro
bigScaryFunc(α, β) {
…😱…
}
Wrap Call
bigScaryFunc(α, β) {
stuffBefore();
bigScaryFunc__(α, β);
stuffAfter();
}
bigScaryFunc__(α, β) {
…😱…
}

23. VictorRentea.ro
No Boulean Parameters

24. VictorRentea.ro
1. Rename
2. Inline
3. Reorder Params
4. Remove Params by extracting more (with Ctrl-Z)
5. Distill switch expressions to Clean Switch Rules
6. Early return errors
7. Add parameters for reuse by extract/inline variable at call site (Ctrl-Z)
8. Move method to object (vs Feature Envy)
9. Encapsulate conditionals
10. Extract static Util functions
11. Spawn Value Objects to host extracted logic
12. Extract again - boolean vs SRP
13. Wrap call to “safely” add more code (Open-Closed Principle)
14. Extract Method Object for heavy logic
15. Extract Pure Functions

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