Clean Code with Java 8 - Functional Patterns and Best Practices

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My talk about how the Clean Code principles and techniques apply/change when you start using functional programming with Java 8. Presented in Paris at Devoxx FR 2018

Software

#DevoxxFR @victorrentea
Clean Code with Java 8
Functional Patterns and Best Practices
- live coding marathon -
Victor Rentea
VictorRentea@gmail.com
www.VictorRentea.ro
1

Victor Rentea
13 years of Java
Lead Architect at IBM
Tech Team Lead and Consultant
Clean Code Evangelist
VictorRentea@gmail.com www.VictorRentea.ro
Krakow Vienna Sofia Casablanca Bucharest Iasi Belgrade Kiew Paris Moscow Barcelona

#DevoxxFR @victorrentea
 Spring
 Hibernate
 Clean Code, Architectures
 Java 8, Design Patterns
 Unit Testing
 Java Performance
 Scala & more...
Independent
Technical Trainer
VictorRentea@gmail.com VictorRentea.ro
1000+ developers
1500+ hours
since 2013
tough clients:

#DevoxxFR @victorrentea
Not Convinced?
5

#DevoxxFR @victorrentea
Let's CODE !!
9
I'll push everything here:
https://github.com/victorrentea/clean-code-java8-devoxxfr

#DevoxxFR @victorrentea
The Clean Code Rules
Applied to Java 8
11

#DevoxxFR @victorrentea
Descriptive Names
Best Lambdas are fit, thin one-liners
Extract heavy lambdas into named ::methods
 in the same class
 in the item class
 as static methods
-> {a-nonymous functions
12
Lambdas

#DevoxxFR @victorrentea
Stream Wrecks
1 usecase = 1 single chain of 30 function calls.
Don't do that !
We beg you !
We have children, families,…
Break them using explanatory variables
Small
Methods
Five Lines
13

#DevoxxFR @victorrentea
Optional
Instead: thatOpt.map(myFunction)
No NullableParameters
Avoid Returning Null,Throw Ex
… or return an Optional
PS: don't be afraid of Orcs, Monads, or .flatMap
14

#DevoxxFR @victorrentea
Passing-a-Block
Pass logic to your function
The Funeral of Template Method™
15

#DevoxxFR @victorrentea
Loan Pattern
You work with a resource
that is managed for you
Decouples real logic from infra code
16

#DevoxxFR @victorrentea
Execute Around Pattern
Explicit AOP
~ Proxy™ or Decorator™
17

#DevoxxFR @victorrentea
Avoid Checked Exceptions
java.util.function interfaces don't declare any throws
Which is good !
You shall suffer if you work with non-Runtime Exceptions!
But if you insist:
- Define throwing functional interfaces
- Use libraries: jool, vavr...
18

#DevoxxFR @victorrentea
Type-specific Logic
switch
Switch Hunt Day®
Hope to find them all: JDD
Simplest to Read
1 switch = 1 method
case XX: return …
OOP
Extends is BAD
ONE Shot
Children90Movie
enum
Isolated Logic
In enum methods
Logic with Dependencies
Function references on enums
(bean passed as param)
19

#DevoxxFR @victorrentea
Merci
20
@victorrentea
VictorRentea@gmail.com
www.VictorRentea.ro
Disclaimer: The use of ® or
™ is the slides is only
anecdotic.
Let's Chat:

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Decades ago, IT started as a single engineering practice, but over the years it grew increasingly fragmented. The overspecialization we face today, in the context of a management-first agile transformation leads to a lack of responsibility, blaming games, repeated patching, painful communication overhead, and fulminating costs. The software craftsmanship movement is rising in this post-agile world with professionals that take control of their careers and continuously learn in the pursuit of mastery. But changing mindset requires determined team efforts and communities, especially when working remotely. What techniques and tricks can you use to grow such a culture of learning in your team? Find out from the founder and lead of one of the largest software craftsmanship communities in the world. This talk is about technical culture and attitude.

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Tests are hard to write if the production design is crappy - goes an old saying. Indeed, writing unit tests gives you one of the most comprehensive, yet brutal, feedback about the design of your production code, but if it comes too late, many developers can’t take it and they will either stop testing or test superficially. At the other end, others struggle to write contrieved, fragile tests full of mocks that end up frustrating more than helping them. This talk reviews the main hints that unit tests provide you, from the most obvious improvements to some of the most subtle design principles.

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aaaaThis presentation focuses on two of the most advanced design tools in your toolbox, whatever the language or framework you might be using. After understanding the basics, we'll see how these concepts can be used in real-world scenarios to simplify those several most complex use-cases in your application. At the end of a mix of slides and live-coding, you'll finally understand the power of these ideas and become prepared to apply them in your day-to-day work. Along the way, we'll introduce concepts like Side Effects, Idempotency, Referential Transparency, Pure Functions and Deep/Shallow Immutability. Also, we'll talk about the powerful Functional Code / Imperative Shell architecture that you can use for your complex workflows. Prepare for an entertaining, highly interactive session that will answer all your questions. Written in Java and spoken in English.

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Clean Code with Java 8 - Functional Patterns and Best Practices

1. #DevoxxFR @victorrentea Clean Code with Java 8 Functional Patterns and Best Practices - live coding marathon - Victor Rentea VictorRentea@gmail.com www.VictorRentea.ro 1

3. Victor Rentea 13 years of Java Lead Architect at IBM Tech Team Lead and Consultant Clean Code Evangelist VictorRentea@gmail.com www.VictorRentea.ro Krakow Vienna Sofia Casablanca Bucharest Iasi Belgrade Kiew Paris Moscow Barcelona

4. #DevoxxFR @victorrentea  Spring  Hibernate  Clean Code, Architectures  Java 8, Design Patterns  Unit Testing  Java Performance  Scala & more... Independent Technical Trainer VictorRentea@gmail.com VictorRentea.ro 1000+ developers 1500+ hours since 2013 tough clients:

5. #DevoxxFR @victorrentea Not Convinced? 5

6. They were! Not Convinced?

7. #DevoxxFR @victorrentea Hard-Core Mode

8. #DevoxxFR @victorrentea Hard-Core Mode

9. #DevoxxFR @victorrentea Let's CODE !! 9 I'll push everything here: https://github.com/victorrentea/clean-code-java8-devoxxfr

10. #DevoxxFR @victorrentea

11. #DevoxxFR @victorrentea The Clean Code Rules Applied to Java 8 11

12. #DevoxxFR @victorrentea Descriptive Names Best Lambdas are fit, thin one-liners Extract heavy lambdas into named ::methods  in the same class  in the item class  as static methods -> {a-nonymous functions 12 Lambdas

13. #DevoxxFR @victorrentea Stream Wrecks 1 usecase = 1 single chain of 30 function calls. Don't do that ! We beg you ! We have children, families,… Break them using explanatory variables Small Methods Five Lines 13

14. #DevoxxFR @victorrentea Optional Instead: thatOpt.map(myFunction) No NullableParameters Avoid Returning Null,Throw Ex … or return an Optional PS: don't be afraid of Orcs, Monads, or .flatMap 14

15. #DevoxxFR @victorrentea Passing-a-Block Pass logic to your function The Funeral of Template Method™ 15

16. #DevoxxFR @victorrentea Loan Pattern You work with a resource that is managed for you Decouples real logic from infra code 16

17. #DevoxxFR @victorrentea Execute Around Pattern Explicit AOP ~ Proxy™ or Decorator™ 17

18. #DevoxxFR @victorrentea Avoid Checked Exceptions java.util.function interfaces don't declare any throws Which is good ! You shall suffer if you work with non-Runtime Exceptions! But if you insist: - Define throwing functional interfaces - Use libraries: jool, vavr... 18

19. #DevoxxFR @victorrentea Type-specific Logic switch Switch Hunt Day® Hope to find them all: JDD Simplest to Read 1 switch = 1 method case XX: return … OOP Extends is BAD ONE Shot Children90Movie enum Isolated Logic In enum methods Logic with Dependencies Function references on enums (bean passed as param) 19

20. #DevoxxFR @victorrentea Merci 20 @victorrentea VictorRentea@gmail.com www.VictorRentea.ro Disclaimer: The use of ® or ™ is the slides is only anecdotic. Let's Chat:

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