1.
NO EXCUSES,
SWITCH TO KOTLIN

2.
NO EXCUSES,
SWITCH TO KOTLIN
t
Thijs Suijten
Mobile developer @ Q42
@tsuijten

3.
GETTING EVERYBODY ONBOARD
TEAM Q42 CLIENT

4.
val s1: String = "Hello" // Immutable variable
val s2 = "how are you" // Type is inferred
Variables
var s3 = "John" // Mutable variable
s3 = "Thijs" // Assign a different value
// w00t! String Interpolation
println("$s1, $s2 $s3?")
//> Hello, how are you Thijs?

5.
fun reformat(str: String,
normalize: Boolean = true,
upperCase: Boolean = true): String {
...
}
Functions
reformat("Hello world")
reformat("Hello world", false, false)
reformat("Hello world", upperCase = false)
// Single-Expression functions
fun twiceTheFun(x: Int) = x * 2

6.
class Person(val firstName: String,
val age: Int,
val locale: Locale = ENGLISH) {
fun sayHello() = println("Hi $firstName!")
}
Classes
val thijs = Person("Thijs", 34)
thijs.sayHello() // Hi Thijs!
class Cat(name: String) {
val name: String = name
}

7.
val x: String? = getSomeOptionalString()
x.length // Does not compile.
Null safety / optionals
val y: String = null // Does not compile.
if (x != null) {
x.length // Compiles!
}
// Safe call
val optLength = foo?.bar?.length // Returns Int?
// Elvis operator.
val length = optLength ?: -1

8.
Data classes
class User(val name: String, val age: Int)
val thijs = User("Thijs", 35)
println(thijs) // User(name=Thijs, age=35)
val bday = thijs.copy(age = 36) // Named params!
println(bday) // User(name=Thijs, age=36)
data

9.
Data classes
public class User {
private String name;
private int age;
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
return name != null ? name.equals(user.name) : user.name == null;
}
@Override public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + age;
return result;
}
@Override public String toString() {
return "User{" +
"name='" + name + ''' +
", age=" + age +
'}';
}
}
// Remember this?
data class User(val name: String, val age: Int)
public class User {
private String name;
private int age;
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
return name != null ? name.equals(user.name) : user.name == null;
}
@Override public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + age;
return result;
}
@Override public String toString() {
return "User{" +
"name='" + name + ''' +
", age=" + age +
'}';
}
}

10.
Functional / lambas
val sum = listOf(1, 2, 3, 4, 5) // 1,2,3,4,5
.filter { number -> number < 5 } // 1,2,3,4
.map { it * 2 } // 2,4,6,8
.sum() // 20
listOf("Zack", "Bob", "Thijs", "Julie", "Rob")
.filter { it.length > 3 } // Zack, Thijs, Julie
.sorted() // Julie, Thijs, Zack

11.
Collections
// Interface List<String>
val fruits = listOf("Apple", "Pear", "Orange")
fruits.add("Strawberry") // Compiler error
// Interface MutableList<String>
val veggies = mutableListOf("Kale", "Spinach", "Lettuce")
veggies.add("Tomato")
veggies += "Cucumber" // Operator overloading

12.
When statement
// Java
if (firstName.equals("Dan")) {
person.setTeam(programmers);
} else if (lastName.equals("Jamie")) {
person.setTeam(designers);
} else {
person.setTeam(others);
}
// Kotlin
when {
firstName == “Dan" -> person.team = programmers
lastName == "Jamie" -> person.team = designers
else -> person.team = others
}

13.
When statement
// Java
switch (firstName) {
case "Dan":
case "Jay":
person.setTeam(programmers);
break;
case "Jamie":
person.setTeam(designers);
break;
default:
person.setTeam(others);
}
// Kotlin
when (firstName) {
"Dan", "Jay" -> person.team = programmers
"Jamie" -> person.team = designers
else -> person.team = others
}

14.
When statement
when (x) {
1 -> print("x = 1")
is Int -> print(x + 1)
is String -> print(x.length + 1)
is IntArray -> print(x.sum())
in 10..20 -> print("Between 10 and 20")
}
val outcome = when(x) {
1 -> "x = 1"
"Hello" -> "is it me you're looking for?"
in 10..20 -> "Between 10 and 20"
}

15.
Extensions
// Java
StringUtils.capitalize(AddressUtils.extractStreet(address))
// Kotlin
address.street.capitalize()
// Extension function
fun String.capitalize() = StringUtils.capitalize(this)
// Extension property
val String.street: String get() = AddressUtils.extractStreet(this)

16.
Kotlin Android extensions
<TextView android:id="@+id/greeting"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<Button android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Click me!"/>
override fun onCreate(savedInstanceState: Bundle?) {
//…
greeting.text = "Hello"
button.onClick { toast("Button clicked!") }
}

17.
Interop Demo

18.
Who is using Kotlin

19.
NO EXCUSES,
SWITCH TO KOTLIN

20.
..
thijs@q42.nl / @tsuijten
try.kotlinlang.org