Introduction to Kotlin

Some basic stuff to show what Kotlin can do better in comparison to Java

Transcript

1. Kotlin type system Variables var name: String = "Salvador"
2. Kotlin type system Variables var name: String = "Salvador" name = "Sanchez"
3. Kotlin type system Variables var name = "Salvador" name = "Sanchez"
4. Kotlin type system Variables var name = "Salvador" name = 21
5. Kotlin type system Variables var name = "Salvador" name = 21 The integer literal does not conform to the expected type String
6. Kotlin type system Variables var name = "Salvador" name = "Sanchez"
7. Kotlin type system Variables - Immutability val name = "Salvador" name = "Sanchez"
8. Kotlin type system Variables - Immutability val name = "Salvador" name = "Sanchez" Val cannot be reassigned
9. Kotlin Functions Declaration fun boilSomeShalgham() {G val shalgham = Shalgham() shalgham.boil() }G
10. Kotlin Functions Declaration fun boilSomeShalgham(): Shalgham {G val shalgham = Shalgham() shalgham.boil() return shalgham }G
11. Kotlin Functions Declaration fun boilSome(shalgham: Shalgham) {G shalgham.boil() }G G
12. Kotlin Functions Default parameters fun boilSome(shalgham: Shalgham) {G shalgham.boil()G }G G
13. Kotlin Functions Default parameters fun boilSome(shalgham: Shalgham, duration: Int) {G shalgham.boil(duration)G }G G boilSome(Shalgham(), 1000)
14. Kotlin Functions Default parameters fun boilSome(shalgham: Shalgham, duration: Int = 1000) {G shalgham.boil(duration) }G G boilSome(Shalgham(), 1000)G
15. Kotlin Functions Default parameters fun boilSome(shalgham: Shalgham, duration: Int = 1000) {G shalgham.boil(duration) }G G boilSome(Shalgham())G
16. Kotlin Functions Default parameters public class ShalghamView extends View { public ShalghamView(Context context) { super(context, null, 0); }G public ShalghamView(Context context, @Nullable AttributeSet attrs) { super(context, attrs, 0); }G public ShalghamView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); }G }G
17. Kotlin Functions Default parameters public class ShalghamView extends View { public ShalghamView(Context context) { super(context, null, 0); }G public ShalghamView(Context context, @Nullable AttributeSet attrs) { super(context, attrs, 0); }G public ShalghamView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); }G }G class ShalghamView : View { constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : super(context, attrs, defStyleAttr) }
18. Kotlin Functions Lambdas view.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { view.setVisibility(View.GONE); } });
19. Kotlin Functions Lambdas view.setOnClickListener({ view: View -> view.visibility = View.GONE })
20. Kotlin Functions Lambdas view.setOnClickListener({ view -> view.visibility = View.GONE })
21. Kotlin Functions Lambdas view.setOnClickListener { view -> view.visibility = View.GONE })
22. Kotlin Functions Lambdas view.setOnClickListener { it.visibility = View.GONE })
23. Kotlin Functions Lambdas view.setOnClickListener { it.visibility = View.GONE }) view.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { view.setVisibility(View.GONE); } });
24. Kotlin Functions Extension Functions class StringUtils { public static String capitalize(String input) { return Character.toUpperCase(input.charAt(0)) + input.substring(1); }G }G
25. Kotlin Functions Extension Functions class StringUtils { public static String capitalize(String input) { return Character.toUpperCase(input.charAt(0)) + input.substring(1); }G }G String capped = StringUtils.capitalize("someString");
26. Kotlin Functions Extension Functions fun String.capitalize() { Character.toUpperCase(get(0)) + substring(1) }G
27. Kotlin Functions Extension Functions fun String.capitalize() { Character.toUpperCase(get(0)) + substring(1) }G
28. Kotlin Functions Extension Functions fun String.capitalize() { Character.toUpperCase(get(0)) + substring(1) }G
29. Kotlin Functions Extension Functions fun String.capitalize() { Character.toUpperCase(get(0)) + substring(1) }G val capped = "someString".capitalize()
30. Kotlin Classes Declaration class Person { val name: String val age: Int constructor(name: String, age: Int) { this.name = name this.age = age } }
31. Kotlin Classes Declaration class Person(val name: String, val age: Int)
32. Kotlin Classes Declaration class Person(val name: String, val age: Int) { fun fly() { print("People can't fly, can they?") }G }G
33. Kotlin Classes Declaration class Person(val name: String, val age: Int) { private fun fly() { print("People can't fly, can they?") }G }G
34. Kotlin Classes Properties class Person { var name: String val age: Int constructor(name: String, age: Int) { this.name = name this.age = age }G }G val person = Person("Salvador", 26) person.name = "Sanchez"
35. Kotlin Classes Properties class Person { var name: String get() { // Return something } set(value) { // Set the value } val age: Int constructor(name: String, age: Int) { this.name = name this.age = age }G }G val person = Person("Salvador", 26) person.name = "Sanchez"
36. Kotlin Classes Data class class Person { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public int getAge() { return age; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Person person = (Person) o; return age == person.age && Objects.equals(name, person.name); } @Override public int hashCode() { return Objects.hash(name, age); } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } }
37. Kotlin Classes Data class data class Person(val name: String, val age: Int)
38. Kotlin Null Safety Optionals var name = "Salvador" name = "Sanchez"
39. Kotlin Null Safety Optionals var name = "Salvador" name = null
40. Kotlin Null Safety Optionals var name = "Salvador" name = null Null cannot be a value of non-null type String
41. Kotlin Null Safety Optionals We crunched anonymized stats from over a 1,000 applications monitored by OverOps’s error analysis micro-agent
42. Kotlin Null Safety Optionals We crunched anonymized stats from over a 1,000 applications monitored by OverOps’s error analysis micro-agent 70% of the production environments that we looked at, NPEs were the most occurred exceptions.
43. Kotlin Null Safety Optionals Tony Hoare “I call it my billion-dollar mistake. It was the invention of the null reference in 1965.
 This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.”
44. Kotlin Null Safety Optionals var name = "Salvador" name = null Null cannot be a value of non-null type String
45. Kotlin Null Safety Optionals var name: String? = "Salvador" name = null
46. Kotlin Null Safety Optionals val name: String? = null
47. Kotlin Null Safety Optionals val name: String? = null print(name.length)
48. Kotlin Null Safety Optionals val name: String? = null if (name != null) { print(name.length) }
49. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G
50. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G
51. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G
52. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G
53. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G fun main(args: Array<String>) { val person: Any = Person() if (person is Person) print(person.age) }G
54. Kotlin Null Safety Smart Cast class Person { public int age = 26; public static void main(String[] args) { Object person = new Person(); if (person instanceof Person) System.out.print(((Person) person).age); }G }G fun main(args: Array<String>) { val person: Any = Person() if (person is Person) print(person.age) }G
55. Kotlin Null Safety Optionals val name: String? = null if (name != null) { print(name.length) }
56. Kotlin Null Safety Optionals val name: String? = null print(name?.length)
57. Kotlin Null Safety Optionals @Nullable private String getAvatarUrl() { if (getUser() != null && getUser().getProfile() != null && getUser().getProfile().getAvatar() != null) { return getUser().getProfile().getAvatar().getUrl(); }G return null; }G
58. Kotlin Null Safety Optionals @Nullable private String getAvatarUrl() { if (getUser() != null && getUser().getProfile() != null && getUser().getProfile().getAvatar() != null) { return getUser().getProfile().getAvatar().getUrl(); }G return null; }G fun getAvatarUrl(): String? { return getUser()?.profile?.avatar?.url }
59. Kotlin Coroutines Coroutines loadToken("resource1") { result -> //Perform some operations with result networkRequest(result) { result2 -> //Some more things to be done on result2 saveToDatabase(result2) { result3 -> //And a lot more for result3 } } }
60. Kotlin Coroutines Coroutines val result = async { loadToken("resource1") }.await() // Perform some operations with result val result2 = async { networkRequest(result) }.await() // Some more things to be done with result2 val result3 = async { saveToDatabase(result2)} // And at last operations with result3
61. Kotlin Coroutines Coroutines suspend fun load(token: String) { val result = loadToken(token) // Perform some operations with result val result2 = networkRequest(result) // Some more things to be done with result2 val result3 = saveToDatabase(result2) // And at last operations with result3 }
62. Kotlin and Java Interoperability Kotlin is 100% interoperable with Java! • Kotlin code can be called directly from Java and vice versa • Kotlin code can live along side Java • Projects can start using Kotlin without any changes to previous
 Java code and/or convert gradually •IDE makes the conversion process easier