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Kotlin presentation

Kotlin Presentation by Cornel Balaban, at Bucharest Mobile Dev Meetup

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Kotlin presentation

  1. 1. 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
  2. 2. 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
  3. 3. 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
  4. 4. 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");
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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()
  9. 9. 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"
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. Useful resources  Must try the "anko" library:  Get dirty with Kotlin Koans here: ask.kt  Try reading Antonio Leiva's Kotlin book:
  15. 15. Oh, and one more thing … adding Kotlin to your project  Not going through all the steps ;)  Check them here: android-studio/
  16. 16. Q &A