Kotlin my way in

Developers, developers, developers.

I’ve always thought that it is amazing what we do - we never settle, we always try to figure out new things, test new things and improve the ones on which we work daily; whether it’s a newly found library, a new architecture pattern that suddenly started to be trending or in this particular case a new language called Kotlin - rejoice!

However those things have different impacts on our projects - using a new library has a different risk than adopting a new language and this is where things get… or as you will hear got really complicated.

For the past years I’ve been trying to evangelise - wololooo - [read this with Age Of Empires priests voice] the people at my company and community into taking the step of gradually start using Kotlin on our applications.

And it hasn’t been an easy task. First, not everyone shares the same enthusiasm in learning something new and secondly making the shift of leaving a language which they know and are familiar with to a new one requires time (both for companies and for people).

Fast forward to the present and currently we have Kotlin code in production, a team thrilled with learning new things and managers glad that all deadlines have been successfully accomplished.

I’m going to share all the steps made (the good and… not so good ones) since I first started to push Kotlin until we have an application ready for production powered by it. Hopefully, without making you fall asleep.

Transcript

1. KOTLIN
   MY WAY IN
   +Carlos Mota
   @cafonsomota
   

   View Slide

2. speakerdeck.com/cmota/kotlin-my-way-in
   

   View Slide

3. View Slide

4. When the QA team starts to teste your app
   NullPointerException
   NullPointerException
   NullPointerException
   NullPointerException
   NullPointerException
   NullPointerException
   NullPointerException
   NullPointerException
   TransactionTooLargeException
   

   View Slide

5. A long time ago in a galaxy far, far away…
   (or roughly four years ago at Coimbra, Portugal)
   

   View Slide

6. 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…
   

   View Slide

7. View Slide

8. A brief history of time
   (when and why it all started)
   

   View Slide

9. 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
   

   View Slide

10. 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
    

    View Slide

11. #10YearChallenge
    

    View Slide

12. HTC Magic
    Android 2.2 (Froyo)
    JAVA 1.5
    Pixel 3
    Android 9.0 (Pie)
    JAVA 1.8
    Kotlin 1.3
    

    View Slide

13. View Slide

14. Kotlin
    - JVM
    - Developed by JetBrains
    - Open source
    - Supported/ used by Google for Android Developed
    - Concise, safe, interoperable, tool-friendly
    (what are we talking about)
    

    View Slide

15. 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”
    

    View Slide

16. (worldwide adoption)
    Kotlin
    

    View Slide

17. 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
    

    View Slide

18. Kotlin
    (worldwide)
    

    View Slide

19. Kotlin
    (worldwide)
    *octoverse.github.com/projects
    Fastest
    2.6xGrowing language
    on GitHub
    more contributors
    

    View Slide

20. 75%
    Kotlin
    (worldwide)
    *insights.stackoverflow.com/survey/2018/
    Second
    most loved language
    on StackOverflow
    of developers
    

    View Slide

21. Actions on Google launched a Java & Kotlin client library (Jan 2019)
    

    View Slide

22. “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
    

    View Slide

23. (behind the scenes)
    Kotlin
    

    View Slide

24. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

25. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

26. Mutability
    etc.
    Null safety
    Default
    values
    Type
    inference
    String
    interpolation
    when
    Collections
    

    View Slide

27. 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
    

    View Slide

28. 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)
    

    View Slide

29. 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
    

    View Slide

30. 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}”)
    

    View Slide

31. 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)
    

    View Slide

32. 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)
    

    View Slide

33. 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)
    

    View Slide

34. NullPointerException
    NullPointerException
    NullPointerException
    NullPointerException
    NullPointerException
    NullPointerException
    NullPointerException
    NullPointerException
    TransactionTooLargeException
    

    View Slide

35. Null Safety
    (language features)
    

    View Slide

36. 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
    

    View Slide

37. Null Safety
    (language features)
    What if I want to use null because of… my legacy code?
    

    View Slide

38. Null Safety
    (language features)
    var result: String
    result = null
    Log.d(TAG, "Result = $result")
    Types are non-null by default
    Safe accessor
    ?
    

    View Slide

39. Null Safety
    (language features)
    var result: String?
    result = null
    val notNull: String = result ?: “hello!”
    result?.let {
    Log.d(TAG, "Result = $result")
    }
    

    View Slide

40. Null Safety
    (language features)
    var result: String?
    result = null
    val notNull: String = result ?: “hello!”
    result?.let {
    Log.d(TAG, "Result = $result")
    }
    Elvis operator
    ?:
    

    View Slide

41. -getOrElse()
    -find()
    -filter()
    -filterNot()
    -filterNotNull()
    -flatMap()
    -mapNotNull()
    -all()
    -any()
    -sumBy()
    -zip()
    -…
    -take()
    -takeLast()
    -sortBy()
    -sortByDescending()
    -groupBy()
    -map()
    Collections
    (language features)
    

    View Slide

42. 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
    

    View Slide

43. 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)
    

    View Slide

44. 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)
    

    View Slide

45. 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)
    

    View Slide

46. 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)
    

    View Slide

47. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

48. “ The best code is no code at all.
    Jeff Atwood
    Coding Horror, StackOverflow, Discourse
    

    View Slide

49. 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
    

    View Slide

50. Concise
    (less code)
    data class Conference (val name: String,
    val location: String,
    val techs: List)
    Conference.kt
    

    View Slide

51. Concise
    (less code)
    65
    1 Kotlin
    JAVA
    lines of code
    line of code
    

    View Slide

52. Concise
    (less code)
    findViewById(R.id.btn_done).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
    //Do something
    }
    });
    .java
    

    View Slide

53. Concise
    (less code)
    findViewById(R.id.btn_done).setOnClickListener {
    //Do something
    }
    .kt
    

    View Slide

54. Concise
    (less code)
    it
    findViewById(R.id.btn_done).setOnClickListener {
    //Do something
    }
    .kt
    

    View Slide

55. Concise
    (less code)
    But can we do better?
    findViewById(R.id.btn_done).setOnClickListener {
    //Do something
    }
    it
    .kt
    

    View Slide

56. 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
    

    View Slide

57. 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);
    }
    ...
    }
    

    View Slide

58. 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)
    

    View Slide

59. 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
    

    View Slide

60. 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
    

    View Slide

61. 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
    

    View Slide

62. Concise
    (less code)
    androidExtensions {
    experimental = true
    }
    build.gradle
    @Parcelize
    data class Conference (val name: String,
    val location: String,
    val techs: List) : Parcelable
    Conference.kt
    

    View Slide

63. Less bugs!
    Concise
    (less code)
    more free time
    (and happier team… and management)
    

    View Slide

64. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

65. - Small learning curve involved
    - Easily to go from JavaScript/ Swift into Kotlin and back
    Easy to learn
    (from a developer’s point of view)
    

    View Slide

66. 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
    

    View Slide

67. 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
    

    View Slide

68. 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")
    

    View Slide

69. 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."
    }
    

    View Slide

70. 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()
    

    View Slide

71. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

72. 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
    

    View Slide

73. - Language features
    - Concise
    - Easy to learn
    - Interoperable with JAVA
    - Big (growing) community
    Kotlin
    (from a developer’s point of view)
    

    View Slide

74. - 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)
    

    View Slide

75. View Slide

76. Spreading the word
    (wolololol…)
    Spreading the word
    (wolololol…)
    

    View Slide

77. I’m convinced!
    and now?
    

    View Slide

78. We should consider to
    adopt Kotlin in our
    project
    

    View Slide

79. The talk
    

    View Slide

80. The talk
    pre Google I/O 17
    #1
    (I think you all know how this talk went, right?)
    

    View Slide

81. 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?
    

    View Slide

82. NO.
    

    View Slide

83. The talk #2
    2.5 years ago
    (if at first you don’t succeed call it version 1.0 - right?)
    

    View Slide

84. it sure will motivate the team and improve
    productivity
    It is null safe, smart casts, lambdas…
    - Does Google support it?
    me: Yes!
    -
    

    View Slide

85. The talk #3
    2 years ago
    

    View Slide

86. The talk #3
    2 years ago
    

    View Slide

87. Kotlin my way in.
    That’s right!
    

    View Slide

88. Kotlin my way in
    1. Community
    2. Team
    3. Management
    (have a plan)
    

    View Slide

89. 1. Community
    2. Team
    3. Management
    Kotlin my way in
    (have a plan)
    

    View Slide

90. 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
    

    View Slide

91. The talk #3
    1. Community
    2. Team
    3. Management
    (talk with your)
    

    View Slide

92. Why would I want to learn a new language if I
    can do my daily tasks with JAVA?
    “
    Team
    Team member Cupcake
    

    View Slide

93. 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
    

    View Slide

94. 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?
    

    View Slide

95. 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
    

    View Slide

96. The talk #3
    1. Community
    2. Team
    3. Management
    (talk with your)
    

    View Slide

97. Management
    - Advantages of using Kotlin
    Null safety
    Smart casts
    Default values
    Override constructors
    Data classes
    Type inference
    …
    

    View Slide

98. View Slide

99. 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
    

    View Slide

100. Management
     - Features that will be done faster
     More concise language (comparing with JAVA)
     - Improves team motivation
     - Low risk
     

     View Slide

101. Kotlin my way in.
     how we’ve done it
     

     View Slide

102. 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
     

     View Slide

103. 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)
     

     View Slide

104. 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
     

     View Slide

105. View Slide

106. 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.)
     

     View Slide

107. Quotes
     (roughly translated from Portuguese)
     We should refactor the entire app to use
     Kotlin!
     “
     Team member Cupcake
     

     View Slide

108. Quotes
     (roughly translated from Portuguese)
     Kotlin is smart enough to detect some
     programming errors before you hit compile.
     “
     Team member KitKat
     

     View Slide

109. 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
     

     View Slide

110. During code review
     (roughly translated from Portuguese)
     “Many years turning chickens! Great success
     with Kotlin.
     Team member Pie
     

     View Slide

111. 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%
     

     View Slide

112. - 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)
     

     View Slide

113. 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
     

     View Slide

114. +Carlos Mota
     @cafonsomota
     KOTLIN MY WAY IN
     

     View Slide