This presentation takes you through the basic features of Kotlin, how it is different than Java and other programming languages, and what's new in it.

1. What’s new in
otlin
Vipul Asri

2. Overview
● Kotlin is a new programming language from
JetBrains
● First appeared in 2011, stable release 1.0 in Feb,
2016
● “Statically typed programming language”
● Procedural as well as Functional Programming
both
● Google announced official support for Kotlin on
Android at Google I/O, 2017

3. Benefits
● Kotlin compiles to JVM bytecode or JavaScript
● Kotlin programs can use all existing Java
Frameworks and Libraries
● Kotlin can be learned easily
● Automatic conversion of Java to Kotlin with
Android Studio
● Kotlin’s null-safety is great

4. Features

5. Extension Functions
fun String.removeSpaces() { … }
// call to extension function
“Hello, I am Vipul Asri”.removeSpaces()
// output
“Hello,IamVipulAsri”

6. Inter-operable With Java
Java code can be used inside Kotlin code and vice-versa.
class Person {
String name = “Person Nath”
public String getNameWithoutSpace() {
return name.removeSpaces();
}
}

7. Synthetic Extension( bye bye to findViewById() )
Java
class MainActivity extends AppCompatActivity{
TextView studentName;
@Override
protected void onCreate(Bundle
savedInstanceState) {
studentName =
findViewById(R.id.studentName);
studentName.setText("Harshit Dwivedi");
}
}
Kotlin
import
kotlinx.android.synthetic.main.activity_main.*
class KotlinActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState:
Bundle?) {
studentName.text = "Harshit" //That's it!
}
}

8. NPE Safety
var name_1: String = "abc"
name_1 = null // try to assign null, won’t compile.
// To allow nulls, we declare a variable as nullable string
var name_2: String? = "abc"
name_2 = null // no compilation error.
val len = name_1.length // there will be no NPE
val len = name_2.length // error: variable 'name_2' can be null

9. NPE Safety
1. Checking for null in conditions
val len = if (name_2 != null) name_2.length else -1
2. Safe Calls (with ?.)
name_2?.length // name_2.length if name_2 is not null, and null otherwise
3. The !! Operator (for NPE Lovers) - not-null assertion operator (!!)
val l = b!!.length // (!!) converts any value to a non-null type
// and throws an exception if the value is null

10. Coroutines (experimental)
● Threads can easily eat up almost a megabyte of memory.
In this context, we can call coroutines (as per the
documentation) as "lightweight" threads.
● A coroutine is sitting on an actual thread pool, which is
used for background execution.
● It only uses the resources when it needs it.

11. launch{}
val job = launch {
val userString = fetchUserString("1")
val user = deserializeUser(userString)
log(user.name)
}
The wrapped code is dispatched to a background thread, and
the function itself returns a Job instance, which can be used in
other coroutines to control the execution.

12. async{}
val user = async {
val userString = fetchUserString("1")
val user = deserializeUser(userString)
user
}.await()
The async function returns a Defered<T> instance, and calling
await() on it you can get the actual result of the computation.

13. Comparison
Java vs Kotlin

14. No semicolons
Java
System.out.println(“Hello”);
Kotlin
println(“Hello”)

15. Type Declaration
Java
int a = 1;
String s = “abc”;
boolean b;
Kotlin
val a: Int = 1
val s: String = “abc”
val b: Boolean

16. Type Inference
Java
int a = 1;
String s = “abc”;
boolean b;
Kotlin
val a = 1
val s = “abc”
val b: Boolean

17. Object Declaration - No ‘new’
Java
Car car = new Car();
Kotlin
val car = Car()

18. String templates
Java
String s = String.format(“%s
has %d apples, name,
count);
Kotlin
val s = “$name has $count
apples”

19. Functions
Java
String getName(Person person) {
return person.getName();
}
Kotlin
fun getName(person: Person): String {
return person.name
}

20. Expressions body
Java
int sum(int a , int b) {
return a+b;
}
Kotlin
val sum(a: Int , b:Int) = a+b

21. ‘When’ Expression
Java
switch(x) {
case 1: log.info("x == 1"); break;
case 2: log.info("x == 2"); break;
default: log.info("x is neither 1 nor
2");
}
Kotlin
when (x) {
in 0,1 -> print("x is too low")
in 2..10 -> print("x is in range")
!in 10..20 -> print("x outside range")
parseInt(s) -> print("s encodes x")
is Program -> print("It's a program!")
else -> print("None of the above")
}

22. Ranges
Java
IntStream.rangeClosed(1, 5)
.forEach(x -> ...);
Kotlin
for (x in 1..5) { ... }

23. Data Classes
Java
class Address {
final String city;
Address(String n) { city = n; }
String getCity() { return city; }
void setCity(String n) { city = n; }
int equals() { ... }
hashCode() { ... }
toString() { ... }
copy() { ... } }
Kotlin
data class Address(var city:String,
var country:Country)

24. Kotlin 1.2
Sharing Code between
Platforms

25. ● JavaScript target, allowing you to compile Kotlin code to JS and to run it in
your browser
● Reuse code between the JVM and JavaScript
● Business logic of your application once, and reuse it across all tiers of your
application – the backend, the browser frontend and the Android mobile app

27. Thank You!