Slide 1
Slide 1 text
Kotlin:
Not your grandfather’s Java
João Carvalho - @johnkarva - PT.JUG
Slide 2
Slide 2 text
No content
Slide 3
Slide 3 text
No content
Slide 4
Slide 4 text
No content
Slide 5
Slide 5 text
What is Kotlin?
Slide 6
Slide 6 text
No content
Slide 7
Slide 7 text
No content
Slide 8
Slide 8 text
https://try.kotlinlang.org
Slide 9
Slide 9 text
Philosophy
Slide 10
Slide 10 text
Pragmatic
Slide 11
Slide 11 text
Concise
Slide 12
Slide 12 text
Safe
Slide 13
Slide 13 text
Interoperable
Slide 14
Slide 14 text
Tooling
Slide 15
Slide 15 text
Lightweight
868KB runtime
Slide 16
Slide 16 text
No content
Slide 17
Slide 17 text
public class HelloWorld {
public static void main(String... args) {
System.out
.println("Hello world " + args[0]);
}
}
Slide 18
Slide 18 text
fun main(args: Array) {
println("Hello world ${args[0]}")
}
Slide 19
Slide 19 text
Types
Slide 20
Slide 20 text
public void printName(Person person) {
System.out.println(person.getName());
}
Slide 21
Slide 21 text
public void printName(Person person) {
System.out.println(person.getName());
}
null
Slide 22
Slide 22 text
No content
Slide 23
Slide 23 text
fun printName(person: Person) {
println(person.name)
}
Slide 24
Slide 24 text
printName(null)
ERROR: Null cannot be a value of
non-null type Person.
Slide 25
Slide 25 text
fun printName(person: Person?) {
if (person != null) {
println(person.name)
}
}
Slide 26
Slide 26 text
Primitive Types
Slide 27
Slide 27 text
Arrays
Slide 28
Slide 28 text
Variables
Slide 29
Slide 29 text
final String name = "Kotlin";
int age = 5;
// A few moments later
age = 6;
Slide 30
Slide 30 text
val name: String = "Kotlin"
var age: Int = 5
// A few moments later
age = 6
Slide 31
Slide 31 text
val name = "Kotlin"
var age = 5
// A few moments later
age = 6
Slide 32
Slide 32 text
Functions/Expressions
Slide 33
Slide 33 text
fun max(one: Int, other: Int): Int {
if (one > other) {
return one
} else {
return other
}
}
Slide 34
Slide 34 text
fun max(one: Int, other: Int): Int {
return if (one > other) {
one
} else {
other
}
}
Slide 35
Slide 35 text
fun max(one: Int, other: Int): Int =
if (one > other) {
one
} else {
other
}
Slide 36
Slide 36 text
fun max(one: Int, other: Int) =
if (one > other) {
one
} else {
other
}
Slide 37
Slide 37 text
fun max(one: Int, other: Int) =
if (one > other) one else other
Slide 38
Slide 38 text
Operators
Slide 39
Slide 39 text
when (x) {
1 -> print("x == 1")
2 -> print("x == 2")
else -> {
print("x is neither 1 nor 2")
}
}
Slide 40
Slide 40 text
Safe Navigation
Slide 41
Slide 41 text
private String safeGetName(Person person) {
return person == null ? null :
person.getName();
}
Slide 42
Slide 42 text
fun safeGetName(person: Person?): String? {
return person?.name
}
Slide 43
Slide 43 text
Elvis Operator
Slide 44
Slide 44 text
fun printName(person: Person?) {
println("Name is ${person?.name
?: "Unknown"}")
}
Slide 45
Slide 45 text
Smart Casts
Slide 46
Slide 46 text
fun printStringLength(any: Any) {
if (any is String) {
println("Length is ${any.length}")
} else {
return println("Oops, not a String")
}
}
Slide 47
Slide 47 text
fun printStringLength(any: Any) {
val asString = any as String
println("Length is ${asString.length}")
}
Slide 48
Slide 48 text
fun printStringLength(any: Any) {
val asString = any as? String
println("Length is ${asString?.length
?: "Unknown"}")
}
Slide 49
Slide 49 text
Classes
Slide 50
Slide 50 text
class Person {
}
Slide 51
Slide 51 text
Final/Public by default
Slide 52
Slide 52 text
Constructors
Slide 53
Slide 53 text
class Fooer(name: String) {
init {
println("Setting up to foo $name")
}
}
Slide 54
Slide 54 text
class Fooer(name: String) {
init {
println("Setting up to foo $name")
}
constructor(name: String, option: String) : this(name) {
println("\tUsing option $option")
}
}
Slide 55
Slide 55 text
Inheritance
Slide 56
Slide 56 text
open class Bar
class Foo : Bar() {
}
Slide 57
Slide 57 text
Properties
Slide 58
Slide 58 text
class Fooer(name: String) {
private val name: String
init {
this.name = name
}
}
Slide 59
Slide 59 text
class Fooer(private val name: String)
Slide 60
Slide 60 text
private var name: String = ""
get() {
println("Returning $name")
return name
}
Slide 61
Slide 61 text
var name: String = ""
private set
Slide 62
Slide 62 text
Delegated Properties
Slide 63
Slide 63 text
class Example {
var p: String by Delegate()
}
Slide 64
Slide 64 text
val lazyValue: String by lazy {
println("computed!")
"Hello"
}
Slide 65
Slide 65 text
var name: String by
Delegates.observable("") {
_, old, new ->
println("$old -> $new")
}
Slide 66
Slide 66 text
Extension Functions
Slide 67
Slide 67 text
fun String.helloize() = "Hello $this"
"World".helloize()
Slide 68
Slide 68 text
Data classes
Slide 69
Slide 69 text
public class Person {
private String name;
private int age;
(...)
}
Slide 70
Slide 70 text
public Person(String name, int age) {
this.name = name;
this.age = age;
}
Slide 71
Slide 71 text
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
Slide 72
Slide 72 text
@Override
public boolean equals(Object o) {
(Stuff generated by your IDE)
}
@Override
public int hashCode() {
int result = name.hashCode();
result = 31 * result + age;
return result;
}
Slide 73
Slide 73 text
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
Slide 74
Slide 74 text
No content
Slide 75
Slide 75 text
data class Person(var name: String,
var age: Int)
Slide 76
Slide 76 text
val john = Person("John", 21)
Slide 77
Slide 77 text
Immutable?
Slide 78
Slide 78 text
private final String name;
public Person withName(String name) {
return new Person(name, this.age);
}
Slide 79
Slide 79 text
data class Person(var name: String,
var age: Int)
Slide 80
Slide 80 text
data class Person(val name: String,
val age: Int)
Slide 81
Slide 81 text
val john = Person("John", 21)
val olderJohn = john.copy(age = 78)
Slide 82
Slide 82 text
Named Arguments
Slide 83
Slide 83 text
public class Person {
public Person(String name,
String lastName,
int age,
Instant birthDate,
(...))
}
Slide 84
Slide 84 text
new Person("John", "Doe",
26, Instant.now(), (...));
Slide 85
Slide 85 text
No content
Slide 86
Slide 86 text
Person(name = "John",
lastName = "Doe",
age = 26,
birthDate = Instant.now())
Slide 87
Slide 87 text
Default Values
Slide 88
Slide 88 text
No content
Slide 89
Slide 89 text
class BCryptPasswordEncoder(
private val strength: Int = -1,
private val random: SecureRandom = SecureRandom()
)
Slide 90
Slide 90 text
Collections
Slide 91
Slide 91 text
Mutable vs Immutable
Slide 92
Slide 92 text
emptyList()
listOf(1, 2, 3)
mutableListOf(1, 2, 3)
emptySet()
setOf("John", "Jane")
mutableSetOf("John", "Jane")
emptyMap()
mapOf("John" to "Doe")
mutableMapOf("John" to "Doe")
Slide 93
Slide 93 text
Utilities
Slide 94
Slide 94 text
// apply
BaseClientDetails().apply {
clientId = "foo"
}
// takeIf
userRepository.findOne("foo")?.takeIf(User::active)
// use
inputStream.use {
it.read()
}
// let
clientId?.let { loadClient(it) }
Slide 95
Slide 95 text
Going Functional
Slide 96
Slide 96 text
Higher-Order Functions
Slide 97
Slide 97 text
fun doWithinLock(lock: Lock,
body: () -> T): T {
lock.lock()
try {
return body()
}
finally {
lock.unlock()
}
}
Slide 98
Slide 98 text
doWithinLock(lock) {
println("Hello lock")
}
Slide 99
Slide 99 text
map.map { (key, value) ->
"$key$value"
}
Slide 100
Slide 100 text
Functions with Receiver
Slide 101
Slide 101 text
class HTML {
var value = ""
fun body(value: String) { this.value = value }
}
fun html(init: HTML.() -> Unit) = HTML().apply {
init()
}
html {
body("Hello world")
}
Slide 102
Slide 102 text
Questions?