Kotlin 101

Dan Nizri

Android Developer @ Yodle

Structure of the talk

1 -> Intro to Kotlin

2 -> Language Features

4 -> Why Android?

3 -> Kotlin vs. Other Languages

5 -> Sample App

6 -> Summary & Sources

1 -> Intro to Kotlin

Why Kotlin?

According to JetBrains

2 -> Language Features

• Lambda expressions + Inline functions = performant custom control structures
• Extension functions
• Null-safety
• Smart casts
• String templates
• Properties
• Primary constructors
• First-class delegation

• Type inference for variable and property types
• Singletons
• Declaration-site variance & Type projections
• Range expressions
• Operator overloading
• Companion objects
• Data classes
• Separate interfaces for read-only and mutable collections

Model Objects

->

Data Classes

Limitations

​

• Cannot be abstract, open, sealed or inner
• Currently cannot extend other classes (but may implement interfaces) -> Kotlin 1.1

Null Safety

• The Billion Dollar Mistake
• Tony Hoare introduced Null references in 1965 “simply because it was so easy to implement”
• Kotlin eliminates NullPointerException
• Null is a first class citizen
• References must be declared as nullable or non-null (default)

Null Safety: Examples

Null Safety: Safe Calls + Chaining

First Class Functions

Higher-Order Functions

• Definition -> A function that does at least one of the following:
• takes a function as an argument
• returns a function as the result
• map(), filter(), reduce(), etc.
• Expressive -> what instead of how

Higher-Order Functions & Lambdas

Extension Functions

• Add functionality to existing class without:
• Modifying the original type
• Creating a new subclass
• Using the Decorator design pattern
• Any class (String, TextView, Context, etc.)
• Resolved statically
• No more Utils classes

Extension Functions: Example 1

Extension Functions: Example 2

Nullable Receiver

3 -> Kotlin vs. Other Languages

Java

• More concise, more safe, first class function support

Scala

• Less complex, better tooling, better interop, Gradle vs. sbt (Scala build tools), not a rewrite of Java

Clojure

• Less functional, closer to Java

Swift

• Similar syntax/features, Java interop, targets JVM

4 -> Why Android?

• Fragmentation of Android OS
• Java 8 release date -> March 2014
• Kotlin can compile to Java 6, 7 or 8
• Comparatively small standard library
• ~10x smaller than Scala lib
• Functions vs. SAM Types
• Inline functions
• Java Interop/Gradle Plugin
• Kotlin Android Extensions

Kotlin Android Extensions: Synthetic Properties

Getting Started

Getting started with Android and Kotlin - JetBrains

5 -> Sample App

https://github.com/yodle/android-kotlin-demo

• Dagger
• Retrofit
• RxKotlin
• RxLifecycle
• RxBinding
• Picasso
• Palette
• RecyclerView
• Custom View
• Kotlin Android Extensions
• Lambas & Higher-Order Functions
• Data Classes
• Extension Functions
• Espresso & Unit Testing

6 -> Summary

Benefits

• Concise
• Safe
• Productive
• Expressive
• Interoperable
• IDE support

Risks

• Less standard
• Smaller community than Java
• Not officially supported by Google
• Build tools, Instant Run

Sources & Interesting Links

• Kotlin Lang Documentation - JetBrains
• Kotlin Koans - JetBrains
• Getting started with Android and Kotlin - JetBrains
• Kotlin's Android Roadmap - JetBrains
• Using Project Kotlin for Android - Jake Wharton
• Android Development with Kotlin (Video) - Jake wharton
• Kotlin for Java Developers (Video) - Virtual Jug
• Why Kotlin is my next programming language - Mike Hearn
• Awesome Kotlin (GitHub) - KotlinBy

Yodle

Lighthouse Field Service

Questions?

Contact: daniel.nizri@yodle.com

Extra Slides

Basic Syntax

Function definition

Mutable local variable

Immutable local variable

Java

Extension Functions: Advanced Example

Anko Library