Kotlin for Java developers.

Transcript

1. Kotlin ve Java’nin yeni versiyonları Hadi Tok @hadi_tok Technical Lead @CitizenMe
2. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
3. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
4. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
5. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
6. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
7. About Kotlin Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. Kotlin is designed to interoperate fully with Java. Kotlin mainly targets the JVM, but also compiles to JavaScript or native code. Source: wikipedia.org / License: WP:CC BY-SA
8. Why Kotlin? Concise Drastically reduce the amount of boilerplate code Source: kotlinlang.org /License: Apache 2.0
9. Why Kotlin? Safe Avoid entire classes of errors such as null pointer exceptions Source: kotlinlang.org /License: Apache 2.0 Source: kotlinlang.org /License: Apache 2.0
10. Why Kotlin? Interoperable Leverage existing libraries for the JVM, Android, and the browser Source: kotlinlang.org /License: Apache 2.0
11. Kotlin for Java Programmers
12. Functions
13. fun main() { println("Hello world!") } Source: kotlinlang.org /License: Apache 2.0
14. fun sum(a: Int, b: Int): Int { return a + b } Source: kotlinlang.org /License: Apache 2.0
15. fun sum(a: Int, b: Int): Int { return a + b } fun sum(a: Int, b: Int) = a + b Source: kotlinlang.org /License: Apache 2.0
16. Default argumnets
17. fun namePrinter(firstName: String, lastName: String) { print("$firstName $lastName") } namePrinter("Hadi", "Tok")
18. fun namePrinter(firstName: String, lastName: String="Tok") { print("$firstName $lastName") } namePrinter("Hadi")
19. Named argumnets
20. fun namePrinter(firstName: String="Hadi", lastName: String="Tok") { print("$firstName $lastName") } namePrinter(lastName = "Hariri")
21. infix notation
22. class MyStringCollection { infix fun add(s: String) { /*...*/ } fun build() { this add "abc" // Correct add("abc") // Correct //add "abc" Incorrect: the receiver must be specified } } Source: kotlinlang.org /License: Apache 2.0
23. Extension Functions
24. fun MutableList<Int>.swap(index1: Int, index2: Int) { val tmp = this[index1] // 'this' corresponds to the list this[index1] = this[index2] this[index2] = tmp } Source: kotlinlang.org /License: Apache 2.0
25. Higher Order Functions
26. class Request { void longRunningOperation(Callback callback) { String result = "result ok"; //assume long running callback.getResult(result); } interface Callback { void getResult(String result); } }
27. Request request =new Request(); request.longRunningOperation(new Callback() { @Override public void getResult(String result) { System.out.println(result); } });
28. class Request{ fun longRunningOperation(callback:(String)->Unit){ val result = "result ok" //assume long running callback(result) } }
29. val request= Request() request.longRunningOperation({result-> print(result) })
30. val request= Request() request.longRunningOperation { result-> print(result) }
31. val request = Request() request.longRunningOperation(this::printResult) fun printResult(result:String){ print(result) }
32. Lambda expressions
33. val sum: (Int, Int) -> Int = { x: Int, y: Int -> x + y } Source: kotlinlang.org /License: Apache 2.0
34. val sum: (Int, Int) -> Int = { x: Int, y: Int -> x + y } sum(3,4) Source: kotlinlang.org /License: Apache 2.0
35. Variables
36. val a: Int = 1 // immediate assignment val b = 2 // `Int` type is inferred Source: kotlinlang.org /License: Apache 2.0
37. var x = 5 // `Int` type is inferred x += 1 Source: kotlinlang.org /License: Apache 2.0
38. Null Safety
39. var a: String = "abc" a = null // compilation error Source: kotlinlang.org /License: Apache 2.0
40. var b: String? = "abc" b = null // ok Source: kotlinlang.org /License: Apache 2.0
41. val l: Int = a.length Source: kotlinlang.org /License: Apache 2.0
42. val l: Int = a.length val m = b.length // error: variable 'b' can be null Source: kotlinlang.org /License: Apache 2.0
43. val c: String? = null val l = if (c != null) c.length else -1 Source: kotlinlang.org /License: Apache 2.0
44. val a = "Kotlin" val b: String? = null println(b?.length) println(a?.length) // Unnecessary safe call Source: kotlinlang.org /License: Apache 2.0
45. val listWithNulls: List<String?> = listOf("Kotlin", null) for (item in listWithNulls) { item?.let { println(it) } //prints Kotlin and ignores null } Source: kotlinlang.org /License: Apache 2.0
46. val l = if (c != null) c.length else -1 Source: kotlinlang.org /License: Apache 2.0
47. val l = if (c != null) c.length else -1 val l = c?.length ?: -1 Source: kotlinlang.org /License: Apache 2.0
48. var b: String? = "abc" val l = b!!.length Source: kotlinlang.org /License: Apache 2.0
49. String Templates
50. var a = 1 // simple name in template: val s1 = "a is $a" a = 2 // arbitrary expression in template: val s2 = "${s1.replace("is", "was")}, now is $a" Source: kotlinlang.org /License: Apache 2.0
51. String Literals
52. val s = "Hello, world!\n" Source: kotlinlang.org /License: Apache 2.0
53. val s = "Hello, world!\n" val text = """ for (c in "foo") print(c) """ Source: kotlinlang.org /License: Apache 2.0
54. val s = "Hello\nworld!" val text = """ for (c in "foo") print(c) """ val text = """ |Tell me and I forget. |Teach me and I remember. |Involve me and I learn. |(Benjamin Franklin) """.trimMargin() Source: kotlinlang.org /License: Apache 2.0
55. Type checks and automatic casts
56. if (obj is String) { // `obj` is automatically cast to `String` in // this branch return obj.length } Source: kotlinlang.org /License: Apache 2.0
57. if (obj !is String) return null // `obj` is automatically cast to `String` in // this branch return obj.length Source: kotlinlang.org /License: Apache 2.0
58. // `obj` is automatically cast to `String` on the // right-hand side of `&&` if (obj is String && obj.length > 0) { return obj.length } Source: kotlinlang.org /License: Apache 2.0
59. Loops
60. val items = listOf("apple", "banana") for (item in items) { println(item) } Source: kotlinlang.org /License: Apache 2.0
61. for (x in 1..5) { print(x) } Source: kotlinlang.org /License: Apache 2.0
62. for (x in 1..5) { print(x) } for (x in 1..10 step 2) { print(x) } Source: kotlinlang.org /License: Apache 2.0
63. for (x in 1..5) { print(x) } for (x in 1..10 step 2) { print(x) } for (x in 9 downTo 0 step 3) { print(x) } Source: kotlinlang.org /License: Apache 2.0
64. val items = listOf("apple", "banana") var index = 0 while (index < items.size) { println("item at $index is ${items[index]}") index++ } Source: kotlinlang.org /License: Apache 2.0
65. when expression
66. fun describe(obj: Any): String = when (obj) { 1 -> "One" "Hello" -> "Greeting" is Long -> "Long" !is String -> "Not a string" else -> "Unknown" } Source: kotlinlang.org /License: Apache 2.0
67. Collections
68. val fruits = listOf("banana", "avocado") fruits .filter { it.startsWith("a") } .sortedBy { it } .map { it.toUpperCase() } .forEach { println(it) } Source: kotlinlang.org /License: Apache 2.0
69. Classes
70. class Person { var firstName: String var lastName: String constructor(firstName: String, lastName: String) { this.firstName = firstName this.lastName = lastName } }
71. class Person(var firstName: String, var lastName: String)
72. val person = Person("Hadi", "Tok")
73. Getter setter
74. class Person(var firstName: String, var lastName: String){ var name = "$firstName $lastName" }
75. class Person(var firstName: String, var lastName: String) { var name: String get() = "$firstName $lastName" }
76. class Person(var firstName: String, var lastName: String) { var name: String get() = "$firstName $lastName" set(value) { val array = value.split(" ") firstName = array[0] lastName = array[1] } }
77. Data Classes
78. class Person { String firstName; String lastName; }
79. class Person{ private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } }
80. class Person{ private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Person person = (Person) o; return Objects.equals(firstName, person.firstName) && Objects.equals(lastName, person.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } }
81. class Person{ private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Person person = (Person) o; return Objects.equals(firstName, person.firstName) && Objects.equals(lastName, person.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } @Override public String toString() { return "Person{" + "firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + '}'; } }
82. class Person(var firstName: String, var lastName: String)
83. data class Person(var firstName: String, var lastName: String)
84. Sealed classes
85. sealed class Result() data class Success(val value: String) : Result() data class Failure(val e: Exception) : Result()
86. when(expr) { is Success -> println(result.value) is Failure -> println(result.e.message) // the else is not required because covered all the cases }
87. Objects
88. object PersonPrinter { fun printPerson(person: Person) { print(person.toString()) } }
89. object PersonPrinter { fun printPerson(person: Person) { print(person.toString()) } } PersonPrinter.printPerson(Person("Hadi", "Tok"))
90. Inline classes
91. inline class Address(val value: String)
92. inline class Address(val value: String) object AddressPrinter{ fun printAddress(address: Address){ print(address.value) } }
93. Delegated Properties
94. val lazyValue: String by lazy { println("computed!") "Hello" } fun main() { println(lazyValue) println(lazyValue) } Source: kotlinlang.org /License: Apache 2.0
95. Coroutines
96. fun printer(){ GlobalScope.launch { val result = longRunningOperation() println("result is $result") } } suspend fun longRunningOperation(): String { delay(5000L) return "200" } Source: kotlinlang.org /License: Apache 2.0
97. New Vesions of Java
98. What is new with Java? Java 9 • Private methods in interfaces
99. What is new with Java? Java 10 • var keyword (type inference)
100. var a = "asd"; System.out.println(a);
101. What is new with Java? Java 11 • Local Variable Syntax for Lambda Parameters
102. interface LambdaInterface { abstract void doSomething(String x); } LambdaInterface lambdaInterface = ((String x) -> System.out.println(x) );
103. interface LambdaInterface { abstract void doSomething(String x); } LambdaInterface lambdaInterface = ((var x) -> System.out.println(x) );
104. What is new with Java? Java 12
105. What is new with Java? Java 13
106. What is new with Java? Java 14 • Switch Expressions
107. String result = ""; int number = 0; switch (0) { case 1: case 2: case 3: result = "low"; break; case 4: result = "ok"; break; case 5: case 6: case 7: result = "high"; break; default: result ="unknown"; } System.out.println("result");
108. String result ="" switch (0) { case 1,2,3: result = "low"; break; case 4: result = "ok"; break; case 5,6,7: result = "high"; break; default: result ="unknown"; } System.out.println(result);
109. String result = switch (0) { case 1, 2, 3 -> "low"; case 4 -> "ok"; case 5, 6, 7 -> "high"; default -> "unknown"; }; System.out.println(result);
110. What is new with Java? Java 15 and later • Text Blocks
111. String html = """ <html> <body> <p>Hello, world</p> </body> </html> """; Source: http://openjdk.java.net/jeps/368
112. String html = """ <html> <body> <p>Hello, world</p> </body> </html> """; Source: http://openjdk.java.net/jeps/368
113. String html = """ <html> <body> <p>Hello, world</p> </body> </html> """; Source: http://openjdk.java.net/jeps/368
114. What is new with Java? Java 15 and later • Text Blocks • Pattern Matching for instanceof
115. if(obj instanceof String){ String s = (String) obj; System.out.println(s); }
116. if(obj instanceof String s){ System.out.println(s); }
117. What is new with Java? Java 15 and later • Text Blocks • Pattern Matching for instanceof • Records
118. record Person(String firstName, String lastName) { } Source: http://openjdk.java.net/jeps/368
119. record Person(String firstName, String lastName) { } Person p = new Person("Hadi", "Tok"); Source: http://openjdk.java.net/jeps/368
120. record Person(String firstName, String lastName) { } Person p = new Person("Hadi", "Tok"); System.out.println(p.firstName() + " " + p.lastName()); Source: http://openjdk.java.net/jeps/368
121. Questions? Usefull Links • Kotlin web site: ◦ https://kotlinlang.org/ • Try Kotlin ◦ https://play.kotlinlang.org/ • KotlinConf 2019: What's New in Java 19: The end of Kotlin? by Jake Wharton : ◦ https://www.youtube.com/watch?v=te3OU9fxC8U
122. Thank you! Hadi Tok @hadi_tok Technical Lead @CitizenMe