With the announcement on officially supporting Kotlin for Android, this presentation tries to compare Java and Kotlin to encourage people to switch to Kotlin

2. Kurt Renzo Acosta
Research and Development
Engineer for Mobile Apps

3. ● Kotlin is a Russian Island
● Statically-typed Programming Language
● Made by JetBrains
● Started in 2011
● Open Source
What is Kotlin?

4. Why Kotlin?
● Modern. Expressive. Safe
● Readable. Concise
● 100% Interoperable with
Java
● Multiplatform

5. Java
Compiler
Kotlin
Compiler
Bytecode
Java
Kotlin

6. Kotlin
Compiler
JVM
Kotlin
JSNative

7. Tools to use for Kotlin

8. Apps that use Kotlin

9. Kotlin Java
Basic Syntax - Variables
var hello = "Hello"
var world: String = "World"
val helloWorld = "Hello World!"
String hello = "Hello";
String world = "World";
final String helloWorld
= "Hello World!";

10. Kotlin Java
Basic Syntax - Comments
// This is a comment
/*
* This is also a comment
*/
// This is a comment
/*
* This is also a comment
*/

11. Kotlin Java
Basic Syntax - If-else
if (a > b) {
println("a")
} else if (b > a) {
println("b")
} else println("c")
if (a > b) {
System.out.println("a");
} else if (b > a) {
System.out.println("b");
} else println("c")

12. Kotlin Java
Basic Syntax - Switch
when (obj) {
"1st" -> println("First")
"2nd" -> println("Second")
else -> println("Third")
}
switch(obj){
case "1st":
System.out.println("First");
break;
case "2nd":
System.out.println("Second");
break;
default:
System.out.println("Third");
}

13. Kotlin Java
Basic Syntax - For Loops
for(x in 1..10){
// ...
}
for(item in items){
// ...
}
for(x in 10 downTo 0){
// ...
}
for((key, value) in map){
// ...
for(int i = 0; i < list.length; i++){
// ...
}
for(Object i : list){
// ...
}
for(Entry i : map){
String key = i.key;
String value = i.value;
// ...
}

14. Kotlin Java
Basic Syntax - While Loops
while(it.hasNext()){
println(it)
}
do{
// This
} while (condition)
while(it.hasNext()){
System.out.println(it);
}
do{
// This
} while (condition);

15. Kotlin Java
Kotlin Features - Classes
class Model(var property: Object)
val model = Model()
model.property = "An Object"
val property = model.property
class Model {
private Object property;
Object getProperty() {
return property;
}
void setProperty(Object property) {
this.property = property;
}
}
Model model = new Model();
model.setProperty("An Object");
Object property = model.getProperty();

16. Kotlin Java
Kotlin Features - Data Classes
data class Model(var property: Object) class Model {
Object property;
Model(Object property){
this.property = property;
}
void setProperty(Object property) {
this.property = property;
}
Object getProperty() {
return property;
}
void equals()(...) {
...
}
}

17. Kotlin Java
Kotlin Features - Objects
object Singleton {
var property
}
var property: Object = Singleton.property
class Singleton {
public Object property;
private static Singleton INSTANCE;
public static Singleton getInstance(){
if(INSTANCE == null) {
INSTANCE = new Singleton();
}
return INSTANCE;
}
}
Object property =
Singleton.getInstance().property;

18. Kotlin Java
Kotlin Features - Objects
var anonymousClass = object {
var x = 5
var y = 5
}
val num = anonymousClass.x
class NotAnonymousClass {
private int x = 5;
private int y = 5;
}
NotAnonymousClass obj =
new NotAnonymousClass();
int x = obj.x;
int y = obj.y;

19. Kotlin Features - Objects
class ClassWithSingleton {
object Singleton {
var property
}
}
val property =
ClassWithSingleton.Singleton.property
class ClassWithSingleton {
companion object {
var property
}
}
val property = ClassWithSingleton.property

20. Kotlin Java
Kotlin Features - Null Safety
var notNullable: String
var nullable: String?
fun main(args: Array<String>) {
notNullable = null //Error
notNullable = "Hi" //OK
nullable = null //OK
nullable = "Hi" //OK
}
String nullable;
public static void main(String[] args){
nullable = null; //OK
nullable = "HI"; //OK
}

21. Kotlin Java
Kotlin Features - Null Safety
var nullable: String?
fun main(args: Array<String>) {
var length = nullable?.length
var forceLength = nullable!!.length
length = nullable.length ?: 0
}
String nullable;
public static void main(String[] args){
int length;
if(nullable != null) {
length = nullable.length();
}
length = nullable != null ?
nullable.length() : 0;
}

22. Kotlin Features - lateinit
var lateString: String = null //Error
fun main(args: Array<String>) {
lateString = "Hello!"
}
lateinit var lateString: String
fun main(args: Array<String>) {
lateString = "Hello!"
}

23. Kotlin Features - lazy loading
var lateString: String = null //Error
fun main(args: Array<String>) {
lateString = "Hello!"
}
val lateString: String by lazy { "Hello!" }

24. Kotlin Features - lazy loading
val greeting: String = null //Error
fun main(args: Array<String>) {
val name = "Kurt"
greeting = "Hello " + name + "!"
}
val greeting: String by lazy {
val name = "Kurt"
"Hello " + name + "!"
}

25. Kotlin Features - String Interpolation
val greeting: String = null //Error
fun main(args: Array<String>) {
val name = "Kurt"
greeting = "Hello $name!"
}
val greeting: String by lazy {
val name = "Kurt"
"Hello $name!"
}

26. Kotlin Features - Named Parameters
fun something(a: Boolean, b: Boolean, c: Boolean, d: Boolean){
return true
}
something(
a = true,
b = true,
c = true,
d = true
)
something(
d = true,
c = true,
b = true,
a = true
)

27. Kotlin Java
Kotlin Features - Default Parameters
fun something(
a: Boolean,
b: Boolean,
c: Boolean = false,
d: Boolean = true
){
return true
}
something(
a = true,
b = true,
)
something(
a = true,
b = true,
c = true
)
Boolean something(Boolean a, Boolean b,
Boolean c, Boolean d) {
return true;
}
Boolean something(Boolean a, Boolean b) {
return something(a, b, false, true);
}
Boolean something(Boolean a, Boolean b,
Boolean c) {
return something(a, b, c, true);
}
something(true, true);

28. Kotlin Java
Kotlin Features - Extension Functions
fun Int.percent(percentage: Int): Int {
return this * (percentage / 100);
}
val num = 100;
num.percent(5)
class IntUtil {
int percent(int value, int percentage) {
return value * (percentage / 100);
}
}
int num = 100;
IntUtil util = new IntUtil();
util.percent(num, 5);

29. Kotlin Java
Kotlin Features - Infix Functions
Infix fun Int.percentOf(value: Int): Int {
return value * (this / 100);
}
val num = 100;
5 percentOf num
class IntUtil {
int percentOf(int value, int percentage) {
return value * (percentage / 100);
}
}
int num = 100;
IntUtil util = new IntUtil();
util.percentOf(num, 5);

30. Kotlin Features - Single-Expression Functions
fun sum(x: Int, y: Int): Int {
return x + y
}
fun checkAndroidVersion(apiLevel: Int):
String {
return when(apiLevel) {
26 -> "Oreo"
25 -> "Nougat"
23 -> "Marshmallow"
21 -> "Lollipop"
...
}
}
fun sum(x: Int, y: Int): Int = x + y
fun checkAndroidVersion(apiLevel: Int): =
when(apiLevel) {
26 -> "Oreo"
25 -> "Nougat"
23 -> "Marshmallow"
21 -> "Lollipop"
...
}
}

31. Kotlin Java
Kotlin Features - Operator Overloading
class Point(val x: Int, val y: Int) {
...
operator fun plus(other: Point): P =
Point(x + other.x, y + other.y)
}
val point1 = Point(5, 10)
val point2 = Point(10, 20)
val point3 = point1 + point2
class Point {
int x;
int y;
...
Point plus(Point point) {
return new Point(this.x + point.x, this.y +
point.y);
}
}
Point point1 = new Point(5, 10);
Point point2 = new Point(16, 15);
Point point3 = point1.plus(point2);

32. Kotlin Java
Kotlin Features - Higher-Order Functions
fun doIfLollipop(func: () -> Unit) {
if(versionIsLollipop){
func()
}
}
doIfLollipop { println("I'm a Lollipop!") }
void doIfLollipop(Runnable callback) {
if(versionIsLollipop){
callback.run();
}
}
doIfLollipop(new Runnable() {
@Override
public void run() {
System.out.println("I'm a Lollipop!");
}
});

33. Kotlin Java
Kotlin Features - Higher-Order Functions
val list: List<Int> =
listOf(1,3,2,4,16,15,32)
list
.filter { it % 2 == 0 }
.map { it * 10 }
List<Integer> list = new ArrayList<>();
list.add(1);
list.add(5);
list.add(3);
list.add(8);
list.add(14);
List<Integer> filteredList = new ArrayList<>();
for(int i = 0; i < list.size(); i++){
if(list.get(i) % 2 == 0){
filteredList.add(list.get(i) * 10);
}
}

34. Q&A