Intro to kotlin

Intro to Kotlin

15.10.2015@Infinum Dino Sulić & Tomislav Homan

Content

● Java on Android - the bad parts

● Alternatives to Java

● Advantages of Kotlin

● (Possible) disadvantages

● Features

● …

● Migration to Kotlin

Content





● Features

● …


Java on Android - the bad parts

● Java 7 was out 2011. - partial support 2013.

● Java 8 was out 2014. - no support announced in the near future

● Null references

● Covariant arrays

● Raw types

● SAM types

● Checked exceptions

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● Features

● …


Alternatives to Java● Xtend - Nice try, but very hard to work with in practice because

of IDE support

● Scala - We are engineers with deadlines, not scientists. Also 80k

methods

● Groovy - Very nice, but not type safe and adds over 30k methods.

IMHO best alternative - to our alternative :)

● Closure, etc, etc…

● Kotlin

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● Features

● …


Advantages of Kotlin (I)● Modern statically typed, object oriented language that borrows

many ideas from functional languages

● Fast learning curve - inspired by Scala and C#. Scaled down

Scala :)

● Meant to be used for building large software systems

● Engineered to be highly interoperable with Java - you can use

existing code base w/o (many) problems

Advantages of Kotlin (II)● The team behind it is JetBrains, creators of IntelliJ which is

Android Studio based on. Also has some contributions from

James Strachan - creator of Groovy

● Significantly more concise and readable than Java, which means

it’s easier to maintain

● Lightweight - Kotlin stdlib has 8k methods

● If it means something to someone - it also compiles to

Javascript

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● Features

● …


(Possible) disadvantages (I)● Code generation - After a long struggle works with, for now,

limited support - Dagger 2 works

● Mocking and testing - managed to run AndroidTestCase with

Mockito, but no serious testing done

● IDE was still bit unstable few months ago, but it seems fine now

and it can only get better. But still be patient for now

(Possible) disadvantages (II)● Java could break when using immutable collections returned

from Kotlin code

● New language that still evolves - teams need to establish code

conventions - still no "Effective Kotlin" :)

● Interoperability with new Jack and Jill compiler - should be all

right, but we have to monitor the situation

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● Features

● …


Features

Selection of features compared to Java

First thing that one will notice is function declaration includes keyword fun

Functions (I)

Parameter types are defined in Scala (Or Swift) way

Functions (II)

Default parameters come in handy

Functions (III)

Named parameters as a good substitution for builders

Functions (IV)

Functions are first-class Kotlin citizens

Functions (V)

Lambdas on Android? Not using Java

Functions (VI)

Lambdas on Android? Kotlin has them

Functions (VII)

Nice Retrofit example - cumbersome using Java

Functions (VIII)

Nice Retrofit example - pretty decent using Kotlin

Functions (IX)

Utility methods vs. extension functions

Functions (X)

Kotlin inferes types

Types (I)

It is difficult to write “final”. Kotlin makes it easier with val keyword

Types (II)

Java fields become Kotlin property. No need for getter / setters unless you want to override them

Properties (I)

If you have the need for some validation…

Properties (II)

...you can still override accessors and access backing field

Properties (III)

Nothing to say here

Null safety (I)

You have to explicitly use nullable type if you want to allow nulls

Null safety (II)

If you use nulls though, safe calls, Elvis and smart casts are here to help

Null safety (III)

Explicit vs. smart casts

Casting

In order to make this business logic right….

Data classes (I)

You have to do some work

Data classes (II)

In order to make this business logic right….

Data classes (III)

...you use data modifier

Data classes (IV)

Typical data repository

Collections (I)

Some business logic

Collections (II)

And lots of error prone work

Collections (III)

Same typical repository

Collections (IV)

Some business logic. Collections are really immutable

Collections (V)

But much less work

Collections (VI)

Just one more example...

Various (I)

...how Kotlin gets some things better

Various (II)

Out of scope● Generics - variance, covariance, contravariance

● Annotations

● Reflection

● Operator overloading

● Type-safe builders

● Dynamic types

● Java interop

● …and lot more

● http://kotlinlang.org/docs/reference/

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● Features

● …


Migration to Koltin● https://kotlinlang.org/docs/tutorials/kotlin-android.html

● Use convert code option - but check thoroughly afterwards

● Use clean code option after upgrading Kotlin version

● KotlinFrontEndException

● > sudo find . -name ".DS_Store" -depth -exec rm {} \;

● This list was much longer few months ago

Software

Intro to kotlin