A Seamless Journey into the Awesome World of

In the beginning...

• I was a Java developer
  • Java 8
  • Big fan of functional programming
• Met a friend at a Dublin Java User Group meetup

Shortly after...

• I started looking into Kotlin

• Youtube "Kotlin for Java Programmers" by Venkat Subramaniam

  • "The took Java and decided to add all the good features they could find, and then they called it Kotlin"
  • "Fluent, elegant syntax"
  • "Wonderful features from a lot of different languages"
  • "A dream come true"

Kotlin History

• Started in 2010 by JetBrains
• They had a huge Java codebase
• Wanted a modern expressive language
• None of the existing languages were a good fit

Kotlin Design Goals

• 100% Java Interoperability
• More readable than Java
• Less error prone than Java
• More productive than Java
• Way simpler than Scala
• Pragmatic
  • Not a research project
  • No ground breaking features
  • Best features established in other languages: groovy, scala, c#

Some time later...

• I started working in Toast!
• Guest and restaurant-facing Android tablets
  • Java & Kotlin
• Backend services
  • ​Java 8 Dropwizard Services
  • Kotlin being used as well
• Internal, guest-facing and restaurant-facing web apps
  • ​Play monolith -> Angular/React

Not long after...

• I was working on the receipts team.
  • Printed receipts (mobile)
  • Digital receipts (web)
  • 1.3 million receipts a day
• ​Refactoring project to extract and rewrite all this code to a shared library.
  • This was all Java

Android Restrictions

• We're restricted to Java 7 on android?
• I can't use Java 8 streams?
  • This sucks.
  • Ok, I guess you can use guavas FluentIterable and RetroLambda, but they're far from elegant
  • Hold on a second, theres no group by operator in guava?
• I saw some Kotlin somewhere in the mobile app, that means I can convert this all to Kotlin, right?

That weekend...

• I converted everything to Kotlin
  • Turns out this is super easy
  • Intellij really helps you along
• Great functional programming features
  • ​Beautiful streams library
  • ​Immutability is the default
  • Final is the default
• I showed the team some before and after highlights
• Kotlin sells itself

But how does all this modern streams stuff work on Java 7 restricted android devices?

• Turns out the Kotlin compiler is awesome!

  • Kotlin can be compiled to any Java version bytecode

  • Kotlin can even be compiled to Javascript

  • Kotlin can even be compiled to native binaries for iOS, OSX, Windows, Linux etc.

For a much more detailed argument for Kotlin see:
Doc by Jake Wharton

Full steam ahead with Kotlin!

Getting started

• Intellij auto-convert to Kotlin
  • Really helps that Jetbrains created Intellij and Kotlin
  • Caveat: you need to be careful with nullability

• Writing Java in Kotlin

  • Which is fine

  • Gradually learn more idomatic Kotlin

• Discover the std lib tools with autocomplete

  • Quickly learn that the stdlib is fantastic
  • Google "is there a more Kotlin way to do this"
• The online documentation is great

Discovering awesome features

• Covers all of the language features really well and in a lot of depth
• Written by two members of the Kotlin team
  • Svetlana Isakova & Dimitri Jemerov

• Big chunks of this book obviated by Kotlin features

Let's get everyone using Kotlin!

Lets organise a series of meetups!

• We'll ramp up people in the office, and engage with the community in Dublin
• Beginner friendly, every 2 weeks
• Start from zero, ramp up, and dive into a fun project

Kotlin Koans

• A series of exercises to get you familiar with the Kotlin syntax and features

• The best way to learn all the language features

• Written by Svetlana Isakova

  • ​Also wrote Kotlin in Action and Atomic Kotlin

Kotlin Koans Introduction Section

Meetup II

Conventions & Collections

Properties, Builders & Generics

Drone Food Delivery

Our Drone

• Bluetooth connected drone

• Parrot Android SDK

• Grabber, Pellet gun, Camera

Drone Delivery

Android Controller

• Control drone with existing android app

  • Take off, Land

  • Control pitch, yaw, roll, etc.

• Converted it to Kotlin & cleaned it up

Drone Commands

• Send higher level commands to drone

  • Move one unit in any direction
  • Fly to coordinate (x, y)
  • Experimented with Coroutines

• Wanted to explore a web framework

• For handling food delivery requests

• Went with Ktor

  • Created by Jetbrains

  • Written in Kotlin

  • For building async web servers & clients

  • Heavily uses coroutines for high scability

  • Really easy to safely async everything

  • Easy to use idomatic api

  • Great testing tools

Create a React-Kotlin app

• Learned how to create a web app using the Kotlin wrappers for React.

• Take advantage of Kotlin features to write expressive code that will compile to a React application

• Really nice Kotlin DSL for building html
   

Using coroutines in your Android App

• Google codelab I did at KotlinConf
• Really great tutorial delivered by Sean McQuillan
• Start with an existing app built with callbacks
• Learn how to convert it to use coroutines

Kotlin Christmas Katas

• Advent of Code challenges

• These are some fun festive challenges

• A great way to pick up new tips and tricks from the Kotlin library, particularly functional programming techniques!

Kotlin in 2018

• In Toast

  • Went from zero usage...
  • To most people using it as their preferred JVM language

• The fastest growing language in 2018

  • 2.6 times the number of github contributors

• One of the most loved languages of 2018

• 5-10 years ahead of Java

• Kotlin 1.3 released

  • Coroutines are stable
  • Kotlin/Native is beta
  • Lots of other improvements

Kotlin in 2018