Slide 1
Slide 1 text
KOTLIN
MY WAY IN
+Carlos Mota
@cafonsomota
Slide 2
Slide 2 text
speakerdeck.com/cmota/kotlin-my-way-in
Slide 3
Slide 3 text
No content
Slide 4
Slide 4 text
When the QA team starts to teste your app
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
TransactionTooLargeException
Slide 5
Slide 5 text
A long time ago in a galaxy far, far away…
(or roughly four years ago at Coimbra, Portugal)
Slide 6
Slide 6 text
me: did you heard about Kotlin?
- Cotton?
me: Kotlin!
- Cotton?
me: Kotlin! The new language developed by JetBrains
- I’ve never heard about it Cotton before.
- But it’s like Cotton Candy? Those people and sweets…
Slide 7
Slide 7 text
No content
Slide 8
Slide 8 text
A brief history of time
(when and why it all started)
Slide 9
Slide 9 text
Android timeline
Android 1.0
HTC Dream
2017
Kotlin 1.3
Kotlin official for Android
2018
2008 2009 2011 2016
2013
Android Studio
Kotlin 1.0
Kotlin announced
Android Runtime
Android Cupcake
HTC Magic
Slide 10
Slide 10 text
JAVA timeline
2004 2011 2014 2017 2018 2019
JAVA 5
2006
JAVA 6 JAVA 7 JAVA 8 JAVA 9 JAVA 10/11 JAVA 12
2016
Android N
(subset of JAVA 8)
2013
JAVA 6
Android KitKat
AS 0.3.2
JAVA 7
AS 3.0
{
{
2 years 2 years
Slide 11
Slide 11 text
#10YearChallenge
Slide 12
Slide 12 text
HTC Magic
Android 2.2 (Froyo)
JAVA 1.5
Pixel 3
Android 9.0 (Pie)
JAVA 1.8
Kotlin 1.3
Slide 13
Slide 13 text
No content
Slide 14
Slide 14 text
Kotlin
- JVM
- Developed by JetBrains
- Open source
- Supported/ used by Google for Android Developed
- Concise, safe, interoperable, tool-friendly
(what are we talking about)
Slide 15
Slide 15 text
Kotlin
(what are we talking about)
Server-side Android Kotlin JS Native
- No runtime overhead
- Lots of new features
- It’s more than just “for Android”
Slide 16
Slide 16 text
(worldwide adoption)
Kotlin
Slide 17
Slide 17 text
5 Reasons Why N26 is Moving to Kotlin
Pat Kua - #CTO of @N26
Square Open Source —s Kotlin
Jake Wharton - Android Google (previous @Square)
How we made Basecamp 3’s Android app 100% Kotlin
Dan Kim - Android @ Basecamp
Slide 18
Slide 18 text
Kotlin
(worldwide)
Slide 19
Slide 19 text
Kotlin
(worldwide)
*octoverse.github.com/projects
Fastest
2.6xGrowing language
on GitHub
more contributors
Slide 20
Slide 20 text
75%
Kotlin
(worldwide)
*insights.stackoverflow.com/survey/2018/
Second
most loved language
on StackOverflow
of developers
Slide 21
Slide 21 text
Actions on Google launched a Java & Kotlin client library (Jan 2019)
Slide 22
Slide 22 text
“We built the client library entirely in Kotlin. We
found Kotlin to be an expressive language with
many features that allow you to implement your
Actions with safer code that is easier to
maintain.
Kishore Subramanian
Software Engineer/Developer relations — Actions on Google
Slide 23
Slide 23 text
(behind the scenes)
Kotlin
Slide 24
Slide 24 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 25
Slide 25 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 26
Slide 26 text
Mutability
etc.
Null safety
Default
values
Type
inference
String
interpolation
when
Collections
Slide 27
Slide 27 text
Mutability
(language features)
val life: Life = Life()
life.answer = 42
life.answer = 100
var answer = 42
answer = 100
val answer = 42
answer = 100
Val cannot be reassigned
Slide 28
Slide 28 text
Mutability
(language features)
val life: Life = Life()
life.answer = 42
life.answer = 100
var answer = 42
answer = 100
var - value can change (mutable)
val - value will never change (immutable)
Slide 29
Slide 29 text
Type inference
(language features)
val life: Life = Life()
life.answer = 42
val life = Life()
life.answer = 42
var answer = 42
answer = 100
var answer = 42
answer = 100L
Type mismatch.
Required: Int
Found: Long
Slide 30
Slide 30 text
String interpolation
(language features)
val life = getAnswerLife()
val universe = getAnswerUniverse()
val everything = getAnswerEverything()
Log.d(TAG, “Life is $life, universe is $universe and everything is $everything”)
Log.d(TAG, "Answer is ${life + universe + everything}”)
Slide 31
Slide 31 text
public int compute(int life) {
return 42;
}
public int compute(int life, int universe) {
return 42;
}
public int compute(int life, int universe, int everything) {
return 42;
}
public void calculateAnswer() {
Log.d(TAG, compute(getAnswerLife());
Log.d(TAG, compute(getAnswerLife(), getAnswerUniverse());
Log.d(TAG, compute(getAnswerLife(), getAnswerUniverse(), getAnswerEverything());
}
Default values
(language features)
Slide 32
Slide 32 text
fun compute(life: Int, universe: Int = 42, everything: Int = 42): Int = 42
fun calculateAnswer() {
Log.d(TAG, compute(getAnswerLife());
Log.d(TAG, compute(getAnswerLife(), getAnswerUniverse());
Log.d(TAG, compute(getAnswerLife(), getAnswerUniverse(), getAnswerEverything());
}
Default values
(language features)
Slide 33
Slide 33 text
fun calculateAnswer() {
...
when (answer) {
1 -> print(“I’m afraid your answer is incorrect Dave.”)
2 -> { print(“Computer says no.”) }
3, 4 -> print(“The error is between the chair and the keyboard.”)
in 5..10 -> print(“Have you tried to turn it on and off?”)
42 -> print(“The answer to life, the universe and everything.”)
else -> print(“Oopsy.”)
}
}
Control flow: when
(language features)
Slide 34
Slide 34 text
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
TransactionTooLargeException
Slide 35
Slide 35 text
Null Safety
(language features)
Slide 36
Slide 36 text
Null Safety
(language features)
var result: String
result = null
Log.d(TAG, "Result = $result")
Null can not be a value of a non-null type String
Types are non-null by default
Slide 37
Slide 37 text
Null Safety
(language features)
What if I want to use null because of… my legacy code?
Slide 38
Slide 38 text
Null Safety
(language features)
var result: String
result = null
Log.d(TAG, "Result = $result")
Types are non-null by default
Safe accessor
?
Slide 39
Slide 39 text
Null Safety
(language features)
var result: String?
result = null
val notNull: String = result ?: “hello!”
result?.let {
Log.d(TAG, "Result = $result")
}
Slide 40
Slide 40 text
Null Safety
(language features)
var result: String?
result = null
val notNull: String = result ?: “hello!”
result?.let {
Log.d(TAG, "Result = $result")
}
Elvis operator
?:
Slide 41
Slide 41 text
-getOrElse()
-find()
-filter()
-filterNot()
-filterNotNull()
-flatMap()
-mapNotNull()
-all()
-any()
-sumBy()
-zip()
-…
-take()
-takeLast()
-sortBy()
-sortByDescending()
-groupBy()
-map()
Collections
(language features)
Slide 42
Slide 42 text
val numbers = mutableListOf(1,2,3)
numbers.add(4)
numbers += 5
val numbers = listOf(1, 2, 3)
numbers.add(4)
Collections
(language features)
immutable list of integers
mutable list of integers
Unresolved reference: add
Slide 43
Slide 43 text
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
.sortedDescending()
> [1, null, 2, null, 3, 4, 5, 6, 7, 8, 9]
Collections
(language features)
Slide 44
Slide 44 text
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
.sortedDescending()
> [1, 2, 3, 4, 5, 6, 7, 8, 9]
Collections
(language features)
Slide 45
Slide 45 text
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
.sortedDescending()
> [2, 4, 6, 8]
Collections
(language features)
Slide 46
Slide 46 text
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
.sortedDescending()
> [8, 6, 4, 2]
Collections
(language features)
Slide 47
Slide 47 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 48
Slide 48 text
“ The best code is no code at all.
Jeff Atwood
Coding Horror, StackOverflow, Discourse
Slide 49
Slide 49 text
public class Conference {
private String mName;
private String mLocal;
private List mTechs;
public Conference(String name, String local, List techs) {
mName = name;
mLocal = local;
mTechs = techs;
}
public String getName() {
return mName;
}
public void setName(String name) {
this.mName = name;
Concise
(less code)
Conference.java
Slide 50
Slide 50 text
Concise
(less code)
data class Conference (val name: String,
val location: String,
val techs: List)
Conference.kt
Slide 51
Slide 51 text
Concise
(less code)
65
1 Kotlin
JAVA
lines of code
line of code
Slide 52
Slide 52 text
Concise
(less code)
findViewById(R.id.btn_done).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something
}
});
.java
Slide 53
Slide 53 text
Concise
(less code)
findViewById(R.id.btn_done).setOnClickListener {
//Do something
}
.kt
Slide 54
Slide 54 text
Concise
(less code)
it
findViewById(R.id.btn_done).setOnClickListener {
//Do something
}
.kt
Slide 55
Slide 55 text
Concise
(less code)
But can we do better?
findViewById(R.id.btn_done).setOnClickListener {
//Do something
}
it
.kt
Slide 56
Slide 56 text
Concise
(less code)
apply plugin: 'kotlin-android-extensions'
btn_done.setOnClickListener { it
//Do something
}
build.gradle
findViewById(R.id.btn_done).setOnClickListener { it
//Do something
}
.kt
Slide 57
Slide 57 text
Concise
(less code)
AppButton.java
public class AppButton extends Button {
public AppButton(Context context) {
super(context);
}
public AppButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
public AppButton(Context context, AttributeSet attrs, int style) {
super(context, attrs, style);
}
...
}
Slide 58
Slide 58 text
Concise
(less code)
public Button(Context context) {
this(context, null);
}
public Button(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.buttonStyle);
}
public Button(Context context, AttributeSet attrs, int defStyleAttr) {
this(context, attrs, defStyleAttr, 0);
}
Button.java (native)
Slide 59
Slide 59 text
Concise
(less code)
class AppButton @JvmOverloads constructor(context: Context,
attrs: AttributeSet? = null,
style: Int = com.android.internal.R.attr.buttonStyle) :
Button(context, attrs, style) {
...
}
AppButton.kt
Slide 60
Slide 60 text
Concise
(less code)
class AppButton @JvmOverloads constructor(context: Context,
attrs: AttributeSet? = null,
style: Int = com.android.internal.R.attr.buttonStyle) :
Button(context, attrs, style) {
...
}
AppButton.kt
default value
Slide 61
Slide 61 text
Concise
(less code)
class AppButton @JvmOverloads constructor(context: Context,
attrs: AttributeSet? = null,
style: Int = com.android.internal.R.attr.buttonStyle) :
Button(context, attrs, style) {
...
}
AppButton.kt
overloads Button.java constructor
Slide 62
Slide 62 text
Concise
(less code)
androidExtensions {
experimental = true
}
build.gradle
@Parcelize
data class Conference (val name: String,
val location: String,
val techs: List) : Parcelable
Conference.kt
Slide 63
Slide 63 text
Less bugs!
Concise
(less code)
more free time
(and happier team… and management)
Slide 64
Slide 64 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 65
Slide 65 text
- Small learning curve involved
- Easily to go from JavaScript/ Swift into Kotlin and back
Easy to learn
(from a developer’s point of view)
Slide 66
Slide 66 text
Kotlin vs Swift
(variables and constants)
var variable = 42
variable = 1
let value = 42
var variable = 42
variable = 1
val value = 42
*adapted from http://nilhcem.com/swift-is-like-kotlin/
Swift
Kotlin
Slide 67
Slide 67 text
let explicitDouble: Double = 70
val explicitDouble: Double = 70.0
Kotlin vs Swift
(explicit types)
*adapted from http://nilhcem.com/swift-is-like-kotlin/
Swift
Kotlin
Slide 68
Slide 68 text
Swift
Kotlin
fun greet(name: String, day: String): String {
return "Hello $name, today is $day."
}
greet(“OPorto", "Saturday")
Kotlin vs Swift
(functions)
*updated from http://nilhcem.com/swift-is-like-kotlin/
func greet(_ name: String,_ day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet(“OPorto", "Saturday")
Slide 69
Slide 69 text
Swift
Kotlin
class Shape {
var numberOfSides = 0
fun simpleDescription() =
"A shape with $numberOfSides sides."
}
Kotlin vs Swift
(classes)
*adapted from http://nilhcem.com/swift-is-like-kotlin/
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
"A shape with \(numberOfSides) sides."
}
Slide 70
Slide 70 text
Swift
Kotlin
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
Kotlin vs Swift
(classes usage)
*adapted from http://nilhcem.com/swift-is-like-kotlin/
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
Slide 71
Slide 71 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 72
Slide 72 text
Interoperable with JAVA
(from a developer point of view)
- @JvmStatic
Generates static methods (for functions) and getter/setters (for properties)
- @JvmOverloads
Generates as many methods as the number of parameters with default values + 1
- @JvmField
The compiler doesn’t generate getter/setters for this property and expose it as a field
Slide 73
Slide 73 text
- Language features
- Concise
- Easy to learn
- Interoperable with JAVA
- Big (growing) community
Kotlin
(from a developer’s point of view)
Slide 74
Slide 74 text
- Good documentation
- A lot of resources
- Internally used by Google’s Android team
- Push forward by Google, JetBrains and the community
Big (growing) community
(from a developer point of view)
Slide 75
Slide 75 text
No content
Slide 76
Slide 76 text
Spreading the word
(wolololol…)
Spreading the word
(wolololol…)
Slide 77
Slide 77 text
I’m convinced!
and now?
Slide 78
Slide 78 text
We should consider to
adopt Kotlin in our
project
Slide 79
Slide 79 text
The talk
Slide 80
Slide 80 text
The talk
pre Google I/O 17
#1
(I think you all know how this talk went, right?)
Slide 81
Slide 81 text
me: Aaaa… not yet?
me: we should start using it on your project because…
me: did you heard about Kotlin?
- Not really - what’s that?
me: A cool new language developed by JetBrains
- Does Google support it?
Slide 82
Slide 82 text
NO.
Slide 83
Slide 83 text
The talk #2
2.5 years ago
(if at first you don’t succeed call it version 1.0 - right?)
Slide 84
Slide 84 text
it sure will motivate the team and improve
productivity
It is null safe, smart casts, lambdas…
- Does Google support it?
me: Yes!
-
Slide 85
Slide 85 text
The talk #3
2 years ago
Slide 86
Slide 86 text
The talk #3
2 years ago
Slide 87
Slide 87 text
Kotlin my way in.
That’s right!
Slide 88
Slide 88 text
Kotlin my way in
1. Community
2. Team
3. Management
(have a plan)
Slide 89
Slide 89 text
1. Community
2. Team
3. Management
Kotlin my way in
(have a plan)
Slide 90
Slide 90 text
Community
Let’s start!
Do you have a
local community
on your town/
nearby?
Meet other enthusiasts
Discuss ideas
Go for a talk/ side project!
kotlinlang.slack
android-pt.slack
Create your own
Slide 91
Slide 91 text
The talk #3
1. Community
2. Team
3. Management
(talk with your)
Slide 92
Slide 92 text
Why would I want to learn a new language if I
can do my daily tasks with JAVA?
“
Team
Team member Cupcake
Slide 93
Slide 93 text
Team
- Comparison between JAVA code with Kotlin code
So they can really see the differences
- It’s faster to develop
More concise language
- It has less crashes
Leave it to the compiler to make it’s initial checks for NPE’s, mutability, etc.
- And is more reliable
We will have more free time
Slide 94
Slide 94 text
Team
- Internal tech talks
- Start small
Don’t just convert your entire code base to Kotlin
- If someone wants to keep with JAVA…
Well, it’s interoperable - so, why not?
Slide 95
Slide 95 text
Keep in mind
- Teams are made by diverse people
- Not everyone will share your enthusiasm
- People are used to JAVA
And all the particular cases of the language
- Learning a new language always requires time and effort
Slide 96
Slide 96 text
The talk #3
1. Community
2. Team
3. Management
(talk with your)
Slide 97
Slide 97 text
Management
- Advantages of using Kotlin
Null safety
Smart casts
Default values
Override constructors
Data classes
Type inference
…
Slide 98
Slide 98 text
No content
Slide 99
Slide 99 text
Management
- More stable application
The compiler identifies errors sooner: NPE’s, mutability, etc.
- Less crashes
- Happier users
- Lower development and bug fixing phases
- More time for other features
Slide 100
Slide 100 text
Management
- Features that will be done faster
More concise language (comparing with JAVA)
- Improves team motivation
- Low risk
Slide 101
Slide 101 text
Kotlin my way in.
how we’ve done it
Slide 102
Slide 102 text
Kotlin my way in
(some raw data)
- project with more than 7 years of daily coding
4755 classes
625487 lines of code
We’re talking about
Slide 103
Slide 103 text
Kotlin my way in
(some raw data)
- project with more than 7 years of daily coding
- low code coverage
- team of 14 developers
- time restrictions
- enthusiasm of a single developer (to start with)
Slide 104
Slide 104 text
Kotlin my way in
(how we’ve done it)
- Risk analysis
Learning curve
Compile time
- JAVA to Kotlin IDE conversion
- Tests made with Kotlin
- Kotlin POC’s
- Time to develop/ productivity
Slide 105
Slide 105 text
No content
Slide 106
Slide 106 text
Kotlin my way in
(how we’ve done it)
- Team of 2 developers + 1 reviewer (redundancy)
Have people from your team onboard
Share knowledge/ discuss ideas
- New feature
- Isolated module
- Integration with external libs (Retrofit, GreenDao, etc.)
Slide 107
Slide 107 text
Quotes
(roughly translated from Portuguese)
We should refactor the entire app to use
Kotlin!
“
Team member Cupcake
Slide 108
Slide 108 text
Quotes
(roughly translated from Portuguese)
Kotlin is smart enough to detect some
programming errors before you hit compile.
“
Team member KitKat
Slide 109
Slide 109 text
During code review
(roughly translated from Portuguese)
“I was fixing an issue on this class and realised
that I would spend less time rewriting it on
Kotlin.
Team member Marshmallow
Slide 110
Slide 110 text
During code review
(roughly translated from Portuguese)
“Many years turning chickens! Great success
with Kotlin.
Team member Pie
Slide 111
Slide 111 text
32%
68% 67%
33%
58%
42%
Nowadays
(stats)
32%
Of the project is now on Kotlin New features written on Kotlin Team developing on Kotlin
58% 67%
Slide 112
Slide 112 text
- Coding conventions
- There’s still a big codebase in JAVA
Does it justifies to be 100% Kotlin
- Coding conventions and backwards support
- Keep moving forward
- Improve on boarding process
Future
(upcoming challenges)
Slide 113
Slide 113 text
Resources
- Android @ Portugal Slack
http://bit.ly/AndroidPTSlack
- Kotlin Official
http://kotlinlang.org/docs/reference/
- Kotlin Training
https://try.kotlinlang.org/
- Kotlin by:
https://jakewharton.com/presentations/
http://antonioleiva.com/kotlin
Slide 114
Slide 114 text
+Carlos Mota
@cafonsomota
KOTLIN MY WAY IN