Kotlin Presentation by Cornel Balaban, at Bucharest Mobile Dev Meetup

2. Who am I?
 Corneliu Balaban
 Mobile Engineering Manager @ Avira Romania
 Android aficionado with BI background
 Catching up on the “Kotlin for iOS” – Swift
 Passionate about BioMedical and AgriTech

3. What is this …
Kotlin?
 It is a Russian Island close
to St. Petersburg
 Initially belong to Sweden
but after Russia annexed it
and …
 Inspired the name for a new
programming language
running in the JVM
 Created by JetBrains,
creators of PhpStorm,
WebStorm, PyCharm etc
 Ads small overhead to the
Android dev env and dex
method count increase by
~6k methods

4. What have we
been missing
inJava?
 No need for functional interfaces in order to implement own
higher functions and lambda’s
 Embedded lists iterators and mapping functions
 Class extensions (well… Swift has them)
 Strongly typed with inferred data types
 No elegant ways of avoiding NPE’s

5. Basic Kotlin
syntax
fun sayHello(name: String): Unit {
print("Hello ${name}!" + "Welcome to Bucharest Mobile Meetup");
}
OR
fun sayHello(name: String): Unit = print("Hello ${name}!" + "Welcome to Bucharest
Mobile Meetup");
OR
fun sayHello(name: String) = print("Hello ${name}!" + "Welcome to Bucharest
Mobile Meetup");

6. OOP concepts
Kotlin classes
 Inherit from Java’s equivalent of Object  Any
 By default are final
 Inheritance is enabled by prefixing the class with "open"
 Primary constructor is embedded in the class signature . It cannot
contain any code
 Secondary constructors are available. Need to delegate to primary
constructor
 init() methods come to the rescue
 Immutable variables are represented by the prefix "val" and can have
inferred data type

7. OOP concepts
Good ol' "bean"
 Easily accessible via "data classes"
 Makes a good separation of code if you want some objects that just
need to hold data
 Can make use of companion objects to hold “static” values

8. MoreOOP …
 Java developers love to be "static"
 Bad luck, there are no class level methods
 "Companion objects" are the new black
 Used to replicate "statics" behavior in Kotlin
 Can be one per class
 Static variables are not available other than via " companion
objects

9. var, val … do I
need to know
them?
 Immutable objects/ variables are prefixed with "val"
 Can be initialized at declaration time. No data type needed as
inference works as a charm
 If they cannot be initialized at declaration time then data type is
mandatory
 Are there other kinds of immutable objects?
 var toDoList1: List<ToDoModel> = listOf(ToDoModel(name="Buy
Milk"),ToDoModel(name="Buy Weed"));
• var toDoList: MutableList<ToDoModel> = mutableListOf()

10. If val reffers to
immutable, do
I have project
level constants
 Compile time constants are defined using
the prefix "const”
 Cannot have a custom getter
 Can be used in annotations
 Can only be of type String or another
primitive
 Can or cannot be part of a class/ object
 Immutable and mutable properties have intrinsic get and set methods
 You can customize the visibility of the setter and or getter as well as their
behavior
 Since properties need to be assigned values at compile time, the only
way to define properties that can receive runtime values is by using the
prefix "lateinit"

11. Optionals &
null safe
accessors
 Swift has them so why not Kotlin as well
 They are some weird implementation of Schroedingers cat
 Optional properties can contain a value or can be null
 Methods can return optionals as well
• To access potentially null variables/ objects you
can use ?.
• In chaining if at least one of the conditions
is null then the entire chained expression is
null

12. Loops,
operator
overloading
and string
interpolation
 Iterating collections is easier with " for – in " loops . No more of the
Java " for – each" nightmare
 Range loops are introduces to help us run code for exact number
of times " for i in 1 .. 27"
 Operator overloading has been made available yet by another
language running on top on the JVM ( as did Groovy)
 String templates and interpolations are yet another valuable

13. Lambdas and
higher order
functions
 Introduced in Java 8 but cumbersome to use.Why?
 Cumbersome to introduce as functional interfaces are needed
 Not backwards compatible
 Not really useful for Android developers as we are still stuck on Java
7
 Lambdas are natively supported by Kotlin
 Kotlin allows methods that can receive other functions as
parameters
 Also it allows the existence of functions outside classes which is
perfect for utils

14. Extensions
 Imagine that "String" would have an … ”getGreetingById" method
 Extensions can be used to add custom methods to existing objects
 They can be called as : Object. getGreetingById(1)
 Very similar to Swift extensions

15. Useful
resources
 Must try the "anko" library: https://github.com/Kotlin/anko
 Get dirty with Kotlin Koans here:
http://try.kotlinlang.org/#/Kotlin%20Koans/Introduction/Strings/T
ask.kt
 Try reading Antonio Leiva's Kotlin book:
https://leanpub.com/kotlin-for-android-developers

16. Oh, and one
more thing …
adding Kotlin
to your project
 Not going through all the steps ;)
 Check them here:
https://blog.jetbrains.com/kotlin/2013/08/working-with-kotlin-in-
android-studio/

17. Q &A