The modern JVM language Kotlin is known to overcome some of Java’s limitations by providing for example null-safety, type inference, data classes and real functions. Last year we built a new online platform for a mentoring organisation 'One Million Mentors' using Kotlin with SpringBoot as API ecosystem. This talk will elaborate the ups and downs of working with Kotlin in a team with high fluctuation of just a few core members and many brilliant volunteers contributing to the project.

1. Kotlin in the
real world
Astrid Ronja Novicky

2. The Challenge

3. Mentoring Platform
New online platform for One Million Mentors
● Mentors and Mentees
● UK based charity
● Scalable and secure

4. Mentoring Platform
New online platform for One Million Mentors
Mentor MC Mentees

5. Mentoring Platform
● Profile creation for mentors and mentoring coordinators
● Training for mentors
● manual online matching

7. The team
● 4 - 5 core team members
● Many volunteers
● on/off boarding

8. UI
API
mySQL
React Redux-
Saga
Kotlin
SpringBoot
Auth0
AWS
EBS
Architecture

9. Architecture
UI
API
mySQL
React Redux-
Saga
Kotlin
SpringBoot
Auth0
AWS
EBS

10. Why Kotlin?

11. Introducing Kotlin
Developed by Jetbrains in 2011
● A better Java?
● A functional language?
● Mainly for Android?

12. Source Code
https://github.com/JetBrains/kotlin/blob/master/docs/contributing.md

14. Kotlin is easy to pick up
● For beginners and for Java & C# developers
● OOP & functional language
● Well documented

15. Benefits
https://kotlinlang.org/

16. Interoperable - Mix and Match

17. Multi purpose

18. Benefits
https://kotlinlang.org/

19. Ecosystem
● Building: Gradle, Maven, Ant
● Frameworks: Spring, Vert.x, Ktor
● ORM: Hibernate
● Testing: JUnit 5, mockito

20. Testing

21. Editors
● IntelliJ IDEA
● Eclipse
● VisualStudioCode
● Vim
● Emacs

22. Benefits
https://kotlinlang.org/

23. Syntax
● Immutable types
● Mutable types
● Type inference
● Property rather than fields
● Define setters and getters

24. Syntax
Collections
● Lists, Sets, Maps
● By default immutable

25. Dataclasses
● Stateful class
● getter/ setters
● Override hashcode / equals
● toString
● copy

26. Dataclasses
getters/setters
@Override hashcode
@Override equals
to String

27. Ports and
Adapters
Domain
Application
Framework HTTPS
mySQL

28. Keeping Domain Model clean

29. REAL functions
● First class citizens
● Function as a type
● Lambda expressions
● Anonymous functions

30. Named and default args

31. No package is private
● Impact on encapsulation
● Classes are public by default
● Package is just a folder/ packing mechanism

32. Benefits
https://kotlinlang.org/

33. Null safety
● No NullPointerExceptions
● Explicitly throw NPE
● !! vs. ?.
● Elvis Operator ?:

34. Null safety

35. Null Pointer Exception

36. Elvis Operator

37. ADT and Pattern matching

38. Would we use
Kotlin again?

39. Yes, we would!
:)

40. Some links for:
https://kotlinlang.org
https://play.kotlinlang.org
https://try.kotlinlang.org

41. Thanks
and stay curious