If you are from Java Back-end world, you think, what is up with all the Kotlin buzz. In this talk, you'll learn why lots of smart developers are making the switch, how easy it is to make that switch, and what is so special about this one comparing to other "promising" JVM languages. If you come from other JVM alternative (like Scala), you think: Hey we already have all these features. How is this different? It is much easier to adopt. In this talk, you'll learn, what you wish your fantastic programming language had too!

1. Don’t try Kotlin
on the Back-end or
You’ll Get Hooked!
by Oleksii Fedorov

2. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
Who am I?
Oleksii Fedorov
• Sr Software Engineer @ Pivotal Berlin
• Entrepreneur In-house @ Pivotal Berlin
• Founder @ iwillteachyoukotlin.com
• Kotlin on Back-end in Production for 2+ years
• Programming for more than 2/3 of my life
• Writer, mentor, coach
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3. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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You don’t have to rewrite
anything

4. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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You don’t have to rewrite anything
1) Add tiny change to your Gradle/Maven build, e.g for Gradle:

5. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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You don’t have to rewrite anything
2) Create your 1st Kotlin file, in same directory with Java files:

6. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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You don’t have to rewrite anything
3) Use your Java (code and libs) from Kotlin, as if it was Kotlin:

7. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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You don’t have to rewrite anything
4) Use your Kotlin (code and libs) from Java, as if it was Java:

8. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Barrier for entry is so low
(so it’s almost a crime to not give it a shot)

9. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Great support on back-end
• Spring (Boot) is fully supported (any recent
version). And since Spring 5 (Boot 2) offers more
concise Kotlinesque APIs
• Vert.x provides dedicated Kotlin support
• Ktor, specifically created for Kotlin, offers high
scalability and easy-to-use idiomatic APIs
• And virtually almost any JVM library

10. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Compile error now > Runtime exception 1 year later

11. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Compiler forces you to handle possible null value:

12. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Instead of “if” statement, leverage safe calls:

13. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Handle edge cases with Elvis operator

14. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Thank you to Kotlin team for Smart-casting:
as opposed to:

15. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Compile-time null-safety
Extension functions and properties on nullable:
“car” is
nullable

16. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Type inference
“car car = new car”
“car entity repository car entity repository = new car entity repository”
we live in the world of redundancy

17. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Type inference
If it is apparent, why repeat?

18. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Type inference
And if it is non-default, then specify it:
(not redundant)

19. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Type inference
Not only variables and properties, return types too:

20. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Type inference
No type inference for function arguments
(because compiler will become insanely slow)
(and your code insanely complicated)

21. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Immutability by default
Variables, properties and collections

22. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Immutability by default
“val” is preferred over “var”

23. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Immutability by default
Collections don’t have modifying methods by default

24. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Immutability by default
And you can make it mutable if you need it

25. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Proper “==”

26. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Named arguments and
default parameter values
Build your own light-weight DSLs

27. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Named arguments
Object factory methods for your test suite where you
specify only things you care about

28. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Default parameter values
Object factory methods for your test suite where you
specify only things you care about

29. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Named arguments
When you want to pass them in order you want

30. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Named arguments and
default parameter values
Find your own usage that improves readability

31. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Less redundancy!

32. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Short syntax for constructors

33. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
33
Boilerplate-less class
definitions
Short syntax for binding constructor parameters to
properties

34. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
34
Boilerplate-less class
definitions
Data classes for your DTOs

35. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Data classes: “==” based on field values

36. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Data classes: “.copy(…)” to create new instance and
modify only few fields:

37. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Data classes: convenient “.toString()”

38. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Data classes: convenient “.hashCode()”

39. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Data classes: de-structuring

40. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Properties: concisely define default getter and setter

41. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Properties: separate visibility of getter & setter

42. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Boilerplate-less class
definitions
Properties: custom implementation of getter/setter

43. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Ever wished this other class
from standard lib had certain
method X?
With extension methods & properties now you can!

44. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Extension methods
It’s like “monkey-patching” (from Ruby)
It’s like “adding method to prototype” (from JS)
but without negative consequences
you have to
import it where
used

45. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Extension properties
When you want to make it feel like accessing a
property
ALT+ENTER auto-
import works here

46. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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Extension methods & props
• No global scope pollution
• They do not modify original classes
• They are basically a syntax sugar:
• Except that you can call them as methods/props

47. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
47
So much more we can talk about
proper function types
“it”
passed
lambdas look like
blocks
lambdas with
receiver for DSLs
+ infix functions

48. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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And more absolutely
amazing for SQL in your
repositories
stop treating
certain things as
exceptions (int, bool)
forgot to handle a
case for enum, use
exhaustive when
just what you want
from a singleton!

49. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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And more

50. Don’t try Kotlin on the Back-end or You’ll Get Hooked!
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I’m covering all of that in:
iwillteachyoukotlin.com/newsletter
bit.ly/2MSsuZG
or
Thank you!
Questions & Answers