The document explores the evolution of programming languages, focusing on Kotlin's advantages over Java, highlighting its modern syntax, null safety, and concise code that enhances productivity. It compares key features of Kotlin with Java, such as immutability, data classes, and safer multithreading features, while emphasizing Kotlin's interoperability with Java. Additionally, it mentions Kotlin's experimental features like coroutines and tools available for developers to enhance their coding experience.

1. KOTLIN
BETTER JAVA
Dariusz Lorenc

2. MY KOTLIN
JOURNEY

3. WHY DO I CARE?

4. JAVA IS EVOLVING SLOWLY
▸ Java 5 - 2005
▸ for each, autoboxing, generics, better concurrency
▸ Java 6 - 2006
▸ Java 7 - 2011
▸ Java 8 - 2014
▸ lambdas, streams
▸ Java 9 - 2017?

5. ” MOST PEOPLE TALK ABOUT JAVA THE LANGUAGE,
AND THIS MAY SOUND ODD COMING FROM ME, BUT
I COULD HARDLY CARE LESS. AT THE CORE OF THE
JAVA ECOSYSTEM IS THE JVM. “
James Gosling,
Creator of the Java Programming Language

6. OTHER JVM LANGUAGES
▸ Groovy
▸ dynamic language
▸ Scala
▸ too many features / steeper learning curve
▸ slow compilation time
▸ too much emphasis on FP?
▸ Clojure
▸ dynamic language, dynamically typed
▸ different syntex, too LISPy?

7. KOTLIN - KEY FEATURES
▸ Statically typed, statically compiled
▸ Built on proven solutions, but simplified
▸ Great Java inter-op
▸ OO at core
▸ FP-friendly
▸ function types
▸ immutability
▸ lets you program in functional style but does not force you

8. ANY BETTER?
▸ Fixes some basic java problems
▸ Draws inspiration from Effective Java
▸ Provides more modern syntax & concepts
▸ Avoids (java’s) boilerplate
▸ Focuses on pragmatism

9. SYNTAX
IN 3 SLIDES

10. VARIABLES / PROPERTIES
var greeting: String
private val hello: String = “hello”
*no static fields/properties

11. FUNCTIONS
fun greet(name: String): String {
return “hello $name”
}
private fun print(name: String) {
println(greet(name))
}
*no static functions

12. CLASSES
class Hello : Greeting {
private val greeting: String = “hello”
override fun greet() {
print(greeting)
}
}

13. WHY DO I CARE
Comparing to Java, Kotlin allows me to write
▸ safer
▸ concise and readable
code, so I can be
‣ more productive
but can still leverage
‣ java’s rich ecosystem
‣ JVM platform

14. SAFER

15. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreeting {
private String greeting;
public JavaGreeting(String greeting) {
this.greeting = greeting;
}
public String getGreeting() {
return this.greeting;
}
}

16. JMM
CAN TRICK YOU

17. KOTLIN - FINAL PROPERTIES
class KotlinGreeting(val greeting: String)

18. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreeting {
private final String greeting;
public JavaGreeting(String greeting) {
this.greeting = greeting;
}
public int length() {
return this.greeting.length();
}
}

19. NPE
#1 EXC. IN PROD

20. KOTLIN - NULL SAFETY
class KotlinGreeting(val greeting: String) {
fun length() = greeting.length
}
class KotlinGreeting(val greeting: String?) {
…
greeting?.length //enforced by compiler
greeting!!.length //enforced by compiler
}

21. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreetings {
private final List<String> greetings;
public JavaGreetings(List<String> greetings) {
if (greetings == null)
throw new NullPointerException();
this.greetings = greetings;
}
public void addGreeting(String greeting) {
this.greetings.add(greeting);
}
}

22. KOTLIN - IMMUTABLE COLLECTIONS
class KotlinGreetings(
private val greetings: List<String>) {
fun addGreeting(greeting: String) {
greetings.add(“hola”) //doesn’t compile
}
}
class KotlinGreetings(
private val greetings: MutableList<String>)

23. JAVA - WHAT COULD POSSIBLY GO WRONG
interface Greeting { }
public class Hello extends Greeting {
public String say() {
return “hello”;
}
}
if (greeting instanceOf Greeting) {
Hello hello = (Hello) greeting
hello.say()
}

24. CLASS CAST
#7 EXC. IN PROD

25. KOTLIN - SMART CAST
if (greeting is Hello) {
greeting.say()
}

26. JAVA - WHAT COULD POSSIBLY GO WRONG
public String say() { return “hello”; }
say() == “hello”

27. KOTLIN - REFERENTIAL EQUALITY
fun say() = “hello”
say() == “hello” //true
say() === “hello” //false
say() !== “hello” //true

28. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreeting {
private final String greeting;
public JavaGreeting(String greeting) {
this.greeting = greeting;
}
public boolean equals(Object aGreeting) {
//some ide-generated code
}
}

29. EQUALS-HASHCODE
CONTRACT

30. KOTLIN - DATA CLASSES
data class KotlinGreeting(val greeting: String)

31. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreeting {
private final String greeting;
public JavaGreeting(String greeting) {
this.greeting = greeting;
}
public boolean equals(JavaGreeting aGreeting) {
//some ide-generated code
}
public int hashCode() {
//some ide-generated code
}
}

32. KOTLIN - OVERRIDE
class KotlinGreeting(val greeting: String) {
//computer says NO!
override fun equals(aGreeting: KotlinGreeting):
Boolean {
…
}
override fun hashCode(): Int {
…
}
}

33. JAVA - WHAT COULD POSSIBLY GO WRONG
public class JavaGreeting {
protected void sayHi() { … }
protected void sayHello() {
}
}
public class HelloGreeting extends JavaGreeting {
protected void sayHi() {
sayHello();
}
}
sayHi();

34. FRAGILE
BASE CLASS

35. KOTLIN - FINAL CLASSES & FUNCTIONS
class KotlinGreeting {
fun sayHi() { … }
fun sayHello() { … }
}
//computer says NO!
class HelloGreeting : KotlinGreeting {
}

36. OTHER SAFETY FEATURES
▸ Serialisable & inner classes
▸ No statics
▸ Functional code
▸ Safer multithreading
▸ More testable code

37. CONCISE &
READABLE

38. CONCISE & NOT READABLE
String one, two, three = two = one = "";
boolean a = false, b = one==two ? two==three : a

39. EXPRESSION BODY
fun greeting(): String {
return “Hello Kotlin”
}
fun greeting(): String = “Hello Kotlin”

40. TYPE INFERENCE
val greeting: String = “Hello Kotlin”
val greeting = “Hello Kotlin”
fun greeting(): String = “Hello Kotlin”
fun greeting() = “Hello Kotlin”

41. CLASS DECLARATION + CONSTRUCTOR + PROPERTIES
class KotlinGreeting(val greeting: String)
public class JavaGreeting {
private final String greeting;
public JavaGreeting(String greeting) {
this.greeting = greeting;
}
public String getGreeting() {
return this.greeting;
}
}

42. NAMED ARGUMENTS - SAY NO TO BUILDERS
class LangGreeting(
val greeting: String,
val lang: String
)
LangGreeting(greeting = “Hello”, lang = “Kotlin”)
LangGreeting(lang = “Java”, greeting = “bye, bye!”)

43. DEFAULT VALUES
class LangGreeting(
val greeting = “Hello”,
val lang: String
)
LangGreeting(lang = “Kotlin”)
LangGreeting(lang = “Java”, greeting = “bye, bye!”)

44. DATA CLASS
data class KotlinGreeting(val greeting: String)
‣ equals()
‣ hashCode()
‣ toString()
‣ copy()
‣ componentN()

45. DATA CLASSES & IMMUTABILITY
data class LangGreeting(
val greeting: String,
val lang: String
)
val kotlinGreeting = LangGreeting(
greeting = “Hello”,
lang = “Kotlin”
)
val javaGreeting = kotlinGreeting.copy(
lang = “Java”
)

46. DATA CLASSES & DESTRUCTURING
data class LangGreeting(
val greeting: String,
val lang: String
)
val (greeting, lang) = kotlinGreeting

47. LAMBDAS
val ints = 1..10
val doubled = ints.map { value -> value * 2 }
val doubled = ints.map { it * 2 }

48. DELEGATION
interface Greeting {
fun print()
}
class KotlinGreeting(val greeting: String) :
Greeting {
override fun print() { print(greeting) }
}
class DecoratedGreeting(g: Greeting) : Greeting by g

49. WHEN EXPRESSION
when (x) {
0, 1 -> print("x == 0 or x == 1")
else -> print("otherwise")
}
val y = when (x) {
0, 1 -> true
else -> false
}

50. CONCISE & READABLE - OTHER FEATURES
▸ Better defaults: final, public?, nested classes are not inner
▸ Extension functions
▸ Default imports
▸ Sealed classes

51. AND THERE IS MORE …
▸ Coroutines - experimental in Kotlin 1.1
▸ Better Kotlin support in Spring 5
▸ Spek
▸ Kotlin/Native
▸ Kotlin to JavaScript
▸ Gradle Kotlin Script

52. JAVA INTEROP & GOTCHAS
▸ Using Java libs in Kotlin is straightforward
▸ Using Kotlin libs in Java
▸ Understand how Kotlin compiles to Java
▸ Final classes - spring, mockito …
▸ mockito-kotlin wrapper
▸ kotlin-allopen & spring plugin
▸ `when` is a keyword
▸ “$” is used for string interpolation

53. REFERENCES
▸ http://kotlinlang.org/docs/reference/
▸ Kotlin in Action [Book]
▸ https://github.com/Kotlin/kotlin-koans
▸ https://try.kotlinlang.org/
▸ https://github.com/KotlinBy/awesome-kotlin

54. Q&A