Kotlin as a Modernized Java @ Oracle Code One 2018

Kotlin was designed with Java developers in mind. Java is evolving, but the language evolution is mostly limited to adding new features. It is nearly impossible to remove features that have proved to be troublesome from a language as popular as Java. This session looks at those features that have been either removed or radically adjusted in Kotlin and how this leads to better, modern, easier-to-read code in Kotlin while still retaining the ability to leverage all the Java libraries in the Java ecosystem.

Transcript

1. Kotlin as a Modernized Java
   Programming in XXI Century
   Presented at JavaOne, 2018
   email elizarov@
   Roman Elizarov
   @relizarov
   

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2. 1995 2003 2004 2011
   

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3. What if Java was designed in 201x?
   

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4. Error handling
   

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5. Error handling
   int res = fread(buf, n, file);
   

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6. Error handling
   int res = fread(buf, n, file);
   if (res < n) { // error or EOF
   if (ferror(file) != 0) {
   // handle error
   }
   return;
   }
   

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7. Error handling
   int res = fread(buf, n, file);
   if (res < n) { … }
   res = fread(buf, m, file);
   if (res < n) { // error or EOF
   if (ferror(file) != 0) {
   // handle error
   }
   return;
   }
   

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8. Exceptions
   try {
   FileInputStream file = new FileInputStream(fileName);
   // …
   int res = file.read(buf, 0, n); // throws exception
   // …
   } catch (IOException e) {
   // handle error
   }
   

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9. Exceptions
   try {
   FileInputStream file = new FileInputStream(fileName);
   // …
   int res = file.read(buf, 0, n);
   // …
   res = file.read(buf, 0, m); // throws exception
   // …
   } catch (IOException e) {
   // handle error
   }
   

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10. Exceptions
    try {
    Data result = work(fileName);
    } catch (IOException e) {
    // handle error
    }
    

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11. Checked Exceptions
    Data work(String fileName) throws IOException {
    FileInputStream file = new FileInputStream(fileName);
    // …
    int res = file.read(buf, 0, n);
    // …
    res = file.read(buf, 0, m);
    // …
    }
    

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13. 1995
    1.0
    2004
    5
    Generics
    

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14. 1995
    1.0
    2004
    5
    Generics
    Lambdas (FP)
    2014
    8
    

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15. Imperative
    List results = new ArrayList<>();
    for (String fileName : fileNames) {
    Result work = work(fileName);
    results.add(work);
    }
    

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16. Func%onal & Declara%ve
    List results = fileNames.stream()
    .map(fileName -> work(fileName))
    .collect(Collectors.toList());
    

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17. Functional + Checked Exceptions = !
    List results = fileNames.stream()
    .map(fileName -> work(fileName))
    .collect(Collectors.toList());
    

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18. XXI Century Languages
    2000 2003
    2005
    2004
    2009 2010 2011 2011
    2012 2014
    

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19. If Java was designed in 201x
    It would not have checked exceptions
    

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20. Func%onal
    

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21. Functional in Java
    List results = fileNames.stream()
    .map(fileName -> work(fileName))
    .collect(Collectors.toList());
    

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22. Functional in Java as an afterthought
    List results = fileNames.stream()
    .map(fileName -> work(fileName))
    .collect(Collectors.toList());
    

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23. Kotlin is designed to be functional
    val results = fileNames
    .map { fileName -> work(fileName) }
    

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24. val results = fileNames
    .map { work(it) }
    

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25. val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    

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26. val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    .doMyProcessing()
    

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27. val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    .doMyProcessing()
    

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28. val results = MyUtils.doMyProcessing(fileNames
    .map { work(it) }
    .filter { it.isGood() })
    

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29. val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    .doMyProcessing()
    

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30. Kotlin extension functions
    val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    .doMyProcessing()
    fun List.doMyProcessing() = …
    

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31. Kotlin top-level functions
    val results = fileNames
    .map { work(it) }
    .filter { it.isGood() }
    .doMyProcessing()
    fun List.doMyProcessing() = …
    

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32. If Java was designed in 201x
    It would have been functional
    by design
    

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33. More generic casualties…
    

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34. More generic casualties…
    List strings = …
    

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35. More generic casualties…
    List strings = …
    List dates = …
    

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36. More generic casualties…
    List strings = …
    List date = …
    List ints = …
    

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37. More generic casualties…
    List strings = …
    List date = …
    List ints = …
    

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38. Primitives
    

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39. C for Consistency
    myDate.toString()
    

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40. C for Consistency
    myDate.toString()
    String.valueOf(myInt)
    

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41. Equality
    myInt == otherInt
    

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42. Equality
    myInt == otherInt
    myString == otherString
    Oops!
    

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43. Equality
    myInt == otherInt
    myString.equals(otherString)
    

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44. If Java was designed in 201x
    It would not have exposed primitives
    

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45. Kotlin hides primi/ves
    myDate.toString()
    myInt.toString()
    

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46. Kotlin hides primitives
    myDate.toString()
    myInt.toString()
    List
    List
    

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47. Kotlin hides primitives
    myDate.toString()
    myInt.toString()
    List
    List
    dates.map { it.toString() }
    ints.map { it.toString() }
    

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48. Kotlin hides primitives
    myDate.toString()
    myInt.toString()
    List
    List
    dates.map { it.toString() }
    ints.map { it.toString() }
    myDate == otherDate
    myInt == otherInt
    

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49. Local variable type inference
    1995
    1.0
    2004
    5
    2018
    10
    2014
    8
    

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50. Before type inference
    int count = …
    double average = …
    List strings = …
    Map> items = …
    

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51. With type inference
    var count = …
    var average = …
    var strings = …
    var items = …
    

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52. With type inference
    var count = …
    var average = …
    var strings = …
    Map> items = …
    

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53. Types on right!
    var count = …
    var average = …
    var strings = …
    var items: Map> = …
    

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54. Where is the type in XXI Century?
    Left Right
    

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55. Where is the type in XXI Century?
    Left Right
    

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56. If Java was designed in 201x
    It would have been designed for type
    inference with types on the right
    

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57. Type safety
    

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58. How type-safe is that?
    int process(List input) { … }
    

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59. How type-safe is that?
    int process(List input) { … }
    

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60. How type-safe is that?
    int process(List input) { … }
    process(null);
    Oops!
    

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61. Null in Kotlin
    fun process(input: List): Int { … }
    process(null)
    

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62. Null in Kotlin is forbidden by default
    fun process(input: List): Int { … }
    process(null)
    

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63. Opt-in to use nulls
    fun process(input: List?): Int { … }
    process(null)
    

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64. fun process(input: List?): Int {
    …
    return input.size
    }
    process(null)
    

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65. fun process(input: List?): Int {
    …
    return input.size
    }
    process(null)
    

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66. fun process(input: List?): Int {
    …
    return input?.size
    }
    process(null)
    

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67. fun process(input: List?): Int {
    …
    return input?.size
    }
    process(null)
    

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68. fun process(input: List?): Int? {
    …
    return input?.size
    }
    process(null)
    

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69. If Java was designed in 201x
    It would have had null-safety
    

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70. How type-safe is that?
    int process(List input) { … }
    

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71. How type-safe is that?
    int process(List input) {
    input.removeIf(data -> !data.isGood());
    return input.size();
    }
    

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72. How type-safe is that?
    int process(List input) {
    input.removeIf(data -> !data.isGood());
    return input.size();
    }
    Oops!
    

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73. Collections in Kotlin
    fun process(input: List): Int {
    input.removeIf { data -> !data.isGood() }
    return input.size
    }
    

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74. Collections in Kotlin are read-only
    fun process(input: List): Int {
    input.removeIf { data -> !data.isGood() }
    return input.size
    }
    

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75. Opt-in to mutability
    fun process(input: MutableList): Int {
    input.removeIf { data -> !data.isGood() }
    return input.size
    }
    

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76. How type-safe is that?
    int process(List input) {
    …
    int size = input.size();
    …
    return size;
    }
    

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77. How type-safe is that?
    int process(List input) {
    …
    final int size = input.size();
    …
    return size;
    }
    

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78. Kotlin: Make val not var
    fun process(input: List): Int {
    …
    val size = input.size
    …
    return size
    }
    

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79. Choice of Defaults
    

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80. Defaults
    Null/Not-null
    

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81. Defaults
    Java
    Null/Not-null Nullable
    

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82. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    

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83. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable
    

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84. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable
    

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85. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    

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86. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final
    

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87. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final Open
    

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88. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final Open Final
    

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89. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final Open Final
    Private/Public
    

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90. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final Open Final
    Private/Public Pkg private
    

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91. Defaults
    Java Real life
    Null/Not-null Nullable Non-nullable
    Mutable/Immutable Mutable Immutable
    Open/Final Open Final
    Private/Public Pkg private Public
    

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92. If Java was designed in 201x
    It would have very different defaults
    

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93. Syntax
    

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94. Semicolon
    foo(); bar();
    

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95. Semicolon
    foo();
    bar();
    

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96. Semicolon
    foo();
    bar();
    

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97. Semicolon
    foo()
    bar()
    

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98. Where is the semicolon in XXI Century?
    Mandatory None/Optional
    

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99. Where is the semicolon in XXI Century?
    Mandatory None/Optional
    

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100. If Java was designed in 201x
     It would have optional semicolon
     

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101. What if Java was designed in 201x?
     ØNo checked exceptions
     ØDesigned for type inference
     ØFunctional by design
     ØNo exposed primitives
     ØNull safety
     ØWell-founded defaults
     ØOptional semicolon
     

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102. Syntactic sugar
     

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103. Properties in Java
     public class Person {
     private String firstName;
     private String lastName;
     public String getFirstName() {
     return firstName;
     }
     public void setFirstName(String firstName) {
     this.firstName = firstName;
     }
     …
     

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104. Properties in Kotlin
     class Person {
     var firstName: String? = null
     var lastName: String? = null
     }
     

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105. Primary constructor in Java
     public class Person {
     private String firstName;
     private String lastName;
     public Person(String firstName, String lastName) {
     this.firstName = firstName;
     this.lastName = lastName;
     }
     …
     

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106. Primary constructor in Kotlin
     class Person(
     var firstName: String?,
     var lastName: String?
     )
     

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107. Primary constructor + null-safety = ❤
     class Person(
     var firstName: String,
     var lastName: String
     )
     

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108. Equals/hashCode/etc in Java
     public class Person {
     private String firstName;
     private String lastName;
     @Override
     public boolean equals(Object o) {
     if (this == o) return true;
     if (!(o instanceof Person)) return false;
     Person person = (Person) o;
     return Objects.equals(firstName, person.firstName) &&
     Objects.equals(lastName, person.lastName);
     }
     …
     

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109. Data class in Kotlin
     data class Person(
     var firstName: String,
     var lastName: String
     )
     

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110. String concatenation in Java
     public class Person {
     @Override
     public String toString() {
     return firstName + " " + lastName;
     }
     …
     

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111. String format in Java
     public class Person {
     @Override
     public String toString() {
     return String.format("%s %s", firstName, lastName);
     }
     …
     

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112. String interpolation in Kotlin
     class Person(…) {
     override fun toString(): String {
     return "$firstName $lastName";
     }
     …
     

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113. String interpolation in Kotlin
     class Person(…) {
     override fun toString(): String =
     "$firstName $lastName"
     …
     

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114. Singleton in Java
     public class Singleton {
     public static final INSTANCE = new Singleton();
     private Singleton() {}
     …
     }
     

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115. Singleton in Kotlin
     object Singleton {
     …
     }
     

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116. Why Kotlin?
     

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117. Kotlin was designed as a modernized Java
     

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118. Kotlin
     ØInteroperability with JVM ecosystem
     ØEasy to learn for Java developers by design
     ØExtensible, DSL-friendly
     ØPragmatic
     ØFun to work with
     

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119. Resources
     Økotlinlang.org
     Øtry.kotlinlang.org
     Ødiscuss.kotlinlang.org
     Øslack.kotlinlang.org
     

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120. Thank you
     Any questions?
     Slides are available at https://speakerdeck.com/elizarov
     email elizarov@
     Roman Elizarov
     @relizarov
     

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