Kotlin is a statically typed programming language that runs on the Java Virtual Machine and is fully interoperable with Java. It was developed by JetBrains as an alternative to Java for Android development, with improvements like null safety, lambdas, and concise syntax. Kotlin aims to be a safer language than Java by eliminating NullPointerExceptions and adding features like data classes, extensions, and higher-order functions. These features allow for more readable, concise code compared to Java.

1. K O T L I N
ANDROID
Kotlin for Android dev

2. 100 % interoperable
with Java
Kotlin for Android devs
Developed by JetBrains
KOTLIN

3. KOTLIN
2010 - Work Started
2011 - Announced
2016 - 1.0 release
2017 - 1.1 release
Official Android First Class Language

4. Agenda
What is Kotlin ?
Kotlin for Android devs
Why Kotlin ?
Syntax crash course
Features of Kotlin
QnA
Hands-on Session

5. https://www.tiobe.com/tiobe-index/
Kotlin is climbing up the ladder

7. • Null references are controlled by the type
system.
• No raw types
• Arrays in Kotlin are invariant
• Kotlin has proper function types, as
opposed to Java’s SAM-conversions
• Use-site variance without wildcards
• Kotlin does not have checked exceptions
Kotlin fixes a series of
issues that Java suffers
from

8. Checked exceptions
Primitive types that are not classes
Static members
Non-private fields
Wildcard-types
What Java has that Kotlin
does not

9. KOTLIN & ANDROID
Kotlin can be updated
independently from the OS.

10. OOP language
with functional
aspects
Modern and
powerful
language
Focuses on
safe concise
and readable
code
Its a statically-typed programming language
What is Kotlin ?
First class tool support

11. Statically typed programming
language for the JVM,
Android and the browser
What is Kotlin ?
Its a statically-typed programming language

12. Statically type

13. What we get by using Java 6/7 + Android -
• Inability to add methods in platform APIs ,
have to use Utils
• NO Lambdas , NO Streams
• NPE - so many of them
What we need
We need modern and smart coding language
Why Kotlin ?

14. • Not Functional language
• Combines OOP and Functional Programming
features
• Open source
• Targets JVM , Android and even JS
Why Kotlin ?

17. Kotlin has lots of advantages for #AndroiDev. By using
#Kotlin, my code is simply better for it. - Annyce Davis
I love #Kotlin. It's a breath of fresh air in the #AndroidDev world
- Donn Felker
At work we're just 100% on the #Kotlin train and yes, that
includes #AndroidDev production code! - Huyen Tue Dao
I enjoy writing in #Kotlin because I don't have to use a lot of
#AndroidDev 3rd party libraries - Dmytro Danylyk
#Kotlin enables more concise and understandable code without sacrificing performance
or safety - Dan Lew

18. Why Kotlin ?

19. Variables and properties
Syntax
val name: String ="John" //Immutable , its final
var name: String ="John" //Mutable
ex: name= "Johnny"
val name ="John" // Types are auto-inferred
val num: int =10 //Immediate assignment
var personList:List<String> = ArrayList() //Explicit type declaration

20. Syntax
Immutable
“Anything which will not change is val”
Mutable
“If value will be changed with time use var”
Rule of thumb

21. Modifiers - Class level
For members declared inside a class :
• Private - member is visible inside the class only.
• Protected - member has the same rules as private but is also available in
subclasses.
• Internal - any member inside the same module can see internal members
• Public - any member who can see the class can see it’s public members.
Default visibility is public

22. Modifiers - Top level
For declarations declared inside at the top level:
• Private - declaration only visible in the same file.
• Protected - not available as the top level is independent of any class
hierarchy.
• Internal - declaration visible only in the same module
• Public - declaration is visible everywhere
Default visibility is public

23. // Simple usage
val myValue = a
if (a < b) myValue = b
// As expression
val myValue = if ( a < b) a else b

24. // when replaces switch operator
when (x) {
1 -> print("First output")
2 -> print("Second output")
else -> {
print(" Nor 1 or 2 ") // This block :)
}

25. // for loop iterates with iterator
val list = listOf("Game of thrones","Breaking Bad","Gotham")
//while and do ..usual
while (x > 0) {
x--
}
do {
val y= someData()
} while( y!=100)

26. // Functions in Kotlin are declared using the fun keyword
fun sum (a: Int , b: Int) : Int {
return a + b
}
//or ..single line return
fun sum(a: Int , b: Int , c: Int) = a + b + c
//default values with functions
fun sum(a: Int , b: Int , c: Int , d: Int = 1) = a + b + c + d

27. Class - big picture
class Person(pName: String) {
var name: String = ""
var age: Int = -1
init {
this.name = pName
}
constructor(pName: String , pAge: Int) : this(pName) {
this.age = pAge
}
fun greet(): String {
return "Hello $name"
}

28. Class - big picture
class Person(pName: String) {
var name: String = ""
var age: Int = -1
init {
this.name = pName
}
constructor(pName: String , pAge: Int) : this(pName) {
this.age = pAge
}
fun greet(): String {
return "Hello $name"
}
// Instance , we call the constructor as if it were a
//regular function
val person = Person()
val me = Person("Adit")
// Kotlin - has no new keyword

29. Code
// The full syntax for declaring a property is
private var age:Int =0
get() = field
set(value) {
if(value>0)
field = value
}
internal fun sum(first: Int , second: Int): Int {
return first + second
}
Access modifier Keyword Name
Param name
Param type
Return type

30. Code
// Full syntax
internal fun sum(first: Int , second: Int): Int {
return first + second
}
// Omit access modifier
fun sum(first: Int , second: Int): Int {
return first + second
}
// Inline return
fun sum(first: Int , second: Int): Int = first + second
// Omit return type
fun sum(first: Int , second: Int) = first + second
// As a type
val sum - { first : Int, second: Int -> first + second }

31. Higher order functions
• Functions which return a function or take a function
as a parameter
• Used via Lambdas
• Java 6 support

32. NULL SAFETY
No more
Kotlin’s type system is aimed to eliminate this
forever.

33. Null Safety
var a: String = "abc"
a = null // compilation error
var b: String? = "abc"
b = null // ok
// what about this ?
val l = a.length // Promise no NPE crash
val l = b.length // error: b can be null

34. Null Safety
// You could explicitly check if b is null , and handle the options separately
val l = if (b!= null) b.length else -1
// Or ...
val length = b?.length
// Even better
val listWithNulls: List<String?> = listOf("A",null)
for (item in listWithNulls) {
item?.let { println(it)
} // prints A ignores null

35. Nullability
• In Java, the NullPointerException is one of the biggest headache’s
• Kotlin , ‘null’ is part of the type system
• We can explicitly declare a property , with nullable value
• For each function, we can declare whether it returns a nullable
value
• Goodbye, NullPointerException

36. Data classes
public class Movie {
private String name;
private String posterImgUrl;
private float rating;
public Movie(String name, String
imageUrl, float rating)
{
this.name = name;
this.posterImgUrl = imageUrl;
this.rating = rating;
}
// Getters and setters
// equals and hashCode
// toString()
}

37. Data classes
// Just use the keyword 'data' and see the magic
data class Movie(val name: String , val imgUrl:
String , val rating: Float)
val inception = Movie("Inception","http://
inception.com/poster.jpg",4.2)
print(inception.name)
print(inception.imgUrl)
print(inception.rating)
// Pretty print
print(inception.toString())
// Copy object
val inceptionTwo = inception.copy(imgUrl= "http://
imageUrl.com/inception2.png")

38. Fun tricks
fun evaluateObject(obj: Any): String {
return when(obj){
is String -> "String it is , ahoy !!"
is Int -> "Give me the 8 ball"
else -> "Object is in space"
}
}
fun ImageView.loadUrl(url: String) {
Glide.with(context).load(url).into(this)
}

39. Extensions
public static boolean isTuesday(Date date) {
return date.getDay() == 2;
}
boolean tuesdayBool =
DateUtils.isTuesday(date);
fun Date.isTuesday(): Boolean {
return getDay() ==2
}
val dateToCheck = Date()
println(date.isTuesday())

40. Lambdas
myButton.setOnClickListener { navigateToDetail() }
fun apply(one: Int , two: Int , func: (Int, Int) -> Int): Int{
return func(one,two)
}
println(apply(1, 2, { a, b -> a * b }))
println(apply(1, 2, { a, b -> a * 2 - 3 * b }))
Higher order Functions

41. if (obj instanceOf MyType) {
((MyType)obj).getXValue();
} else {
// Oh no do more
}
Smart Casting
if (obj is MyType) {
obj.getXValue()
} else {
// Oh no do more
}

42. … and More
• Visibility Modifiers
• Companion Objects
• Nested, Sealed Classes
• Generics
• Coroutines
• Operator overloading
• Exceptions
• Annotations
• Reflection
• and more

43. … and Even More
• Infix extension methods
• Interfaces
• Interface Delegation
• Property Delegation
• Destructuring
• Safe Singletons
• Init blocks
• Enums
• Multiline Strings
• Tail recursion

44. CODE
❤ Kotlin
Try Kotlin online
https://goo.gl/z9Hhq6
https://fabiomsr.github.io/from-java-to-kotlin/

45. QnA

46. THANK YOU
@aditlal