BangaloreJUG introduction to kotlin

Introduction to Kotlin
Feature comparison between J & K
@iChanSek www.chansek.com

About Me
● Working as an Android Engineer since last 6 years

About Me
● Created few apps like Chanse Games, Chanse Shops

About Me
● A failure Entrepreneur

About Me
● Author of an about to be released Kotlin book

About Me
● Only know upto Java-7

About Me
● Worked with Kotlin since last 1 year

About Me
● Organizing Bengaluru’s Kotlin Group - BlrKotlin

About Me
● Organizing Bengaluru’s Kotlin Group - BlrKotlin
● meetup.com/BlrKotlin & blrkotlin.herokuapp.com

Highlights of Kotlin
● Statically typed language like Java

● Billion Dollar mistake is no more as Null is in type system
and treated specially

● 100% interoperable with Java

● Believes in “Sharing is Caring” by supporting multi-
platform

● Believes in “Sharing is Caring” by supporting multi-
platform
● Much more concise than Java

Why should you try Kotlin?
● No need to refactor the whole project.

● Write Less - Maintain Less - Spend Less

● No NPE - Millions of Profit - More Team Budget *

● No NPE - Millions of Profit - More Team Budget *
● Lot of awesome features to write neat code.

final vs val
class Test { 
private String tag = "Test"; 
 
public void test() { 
Log.d(tag, "Testing..."); 
} 
}

final vs val
class Test { 
 
} 
}
class Test { 
private tag = "Test"; 
 
fun test() { 
} 
}
var

final vs val
class Test { 
 
} 
}
class Test { 
 
fun test() { 
} 
}
● final is ignored in Java
var

final vs val
class Test { 
 
} 
}
class Test { 
 
fun test() { 
} 
}
● var is an evil keyword in Kotlin
var

final vs val
class Test { 
 
} 
}
class Test { 
 
fun test() { 
} 
}
● Using var and not updating the value? You will be discouraged until you use val.
var

final vs val
class Test { 
 
} 
}
class Test { 
 
fun test() { 
} 
}
● Using var and not updating the value? You will be discouraged until you use val.
val

final vs open
class Parent { }
class Child extends Parent { }

final vs open
class Parent { }
class Child extends Parent { } class Child extends Parent()
class Parent

final vs open
class Parent { }
● All classes are final by default.
class Parent

final vs open
class Parent { }
● If you want to inherit, you have to plan and design the class
accordingly.
class Parent

final vs open
class Parent { }
● If you want to inherit, you have to plan and design the class
accordingly.
● open keyword does the thing for you.
open class Parent

private means private
public class JavaEncapsulation {
private class Animal { }
private Animal animal;
public Animal getAnimal() {
return animal;
}
public void setAnima(Animal anima) {
this.animal = anima;
}
}

return animal;
}
}
}
class KtEncapsulation {
private var animal = Animal()
fun getAnimal() = animal
fun setAnimal(newAnimal: Animal) {
animal = newAnimal
}
}
private inner class Animal { }

return animal;
}
}
}
animal = newAnimal
}
}
Animal type is private to this class

return animal;
}
}
}
animal = newAnimal
}
}
getAnimal() is public function

return animal;
}
}
}
animal = newAnimal
}
}
Can not expose a private type Animal from
public functions getAnimal() and setAnimal()

return animal;
}
}
}
animal = newAnimal
}
}
inner class Animal { }
Compiles fine as no violation of Encapsulation

concat vs template
public String toString() {
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", phone='" + phone + ''' +
'}';
}

concat vs template
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", phone='" + phone + ''' +
'}';
}
fun toString(): String {
return "User(name='$name',
email='$email', phone='$phone')"
}

concat vs template
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", phone='" + phone + ''' +
'}';
}
}
● String Templating allows to write any expression within the String.

concat vs template
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", phone='" + phone + ''' +
'}';
}
}
● A simple variable can be referred using $ symbol as prefix.

concat vs template
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", phone='" + phone + ''' +
'}';
}
}
● A simple variable can be referred using $ symbol as prefix.
● A complex operation can also be done using ${operation} syntax. For
example - ${email.toUpperCase()}

overloading vs default parameters

int add(int a, int b) {
return a + b;
}
int add(int a, int b, int c) {
return a + b + c;
}
public void testAdd() {
add(10, 20);
add(10, 20, 30);
}

return a + b;
}
return a + b + c;
}
add(10, 20);
add(10, 20, 30);
}
fun add(a: Int, b: Int, c: Int = 0) =
a + b + c
fun testAdd() {
add(10, 20)
add(10, 20, 30)
}

return a + b;
}
return a + b + c;
}
add(10, 20);
add(10, 20, 30);
}
a + b + c
fun testAdd() {
add(10, 20)
add(10, 20, 30)
}
● a and b are usual parameters.

return a + b;
}
return a + b + c;
}
add(10, 20);
add(10, 20, 30);
}
a + b + c
fun testAdd() {
add(10, 20)
add(10, 20, 30)
}
● c is having a default value as 0.

return a + b;
}
return a + b + c;
}
add(10, 20);
add(10, 20, 30);
}
a + b + c
fun testAdd() {
add(10, 20)
add(10, 20, 30)
}
● c is having a default value as 0.
● When no value passed to c, 0 will
be considered.

Type Cast vs Smart Cast
public void print(Animal animal) {
if (animal instanceof Dog) {
Dog dog = (Dog) animal;
S.out.println(dog.toDog());
} else if (animal instanceof Cat) {
Cat cat = (Cat) animal;
S.out.println(cat.toCat());
}
}

}
}
fun print(animal: Animal) {
if (animal is Dog) {
println(animal.toDog())
} else if (animal is Cat) {
println(animal.toCat())
}
}

}
}
}
}
● is more readable than instanceof

}
}
}
}
● if - animal is already a Dog

}
}
}
}
● if - animal is already a Dog
● else if - animal is already a Cat

POJO vs data class
class User {
private String name;
private String email;
private String phone;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public String getEmail() { return email; }
public void setEmail(String email) { this.email = email; }
public String getPhone() { return phone; }
public void setPhone(String phone) { this.phone = phone; }
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
return Objects.equals(name, user.name) &&
Objects.equals(email, user.email) &&
Objects.equals(phone, user.phone);
}
@Override
public int hashCode() {
return Objects.hash(name, email, phone);
}
@Override
return "User{" +

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
data class User(var name: String,
email: String, var phone: String)
var

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
● Just prefix with data keyword and
your POJO is ready.
var

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
your POJO is ready.
● You get getters, setters, equals(),
hashCode() and toString() for free.
var

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
your POJO is ready.
● A copy() also in addition to all.
var

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
your POJO is ready.
● var - both getters and setters
var

POJO vs data class
class User {
@Override
}
@Override
}
@Override
return "User{" +
your POJO is ready.
● var - both getters and setters
● val - only getters
val

Features of Kotlin
Features that are not present in Java

Nullable Types
● Kotlin’s solution to billion dollar mistake.

Nullable Types
● By default everything in Kotlin is non-nullable.

Nullable Types
● If you want to assign null to a variable, you have to declare
that as a nullable.

Nullable Types
that as a nullable.
● Syntax:
● non-nullable - Int, String, User
● nullable - Int?, String?, User?

Nullable Types
that as a nullable.
● Syntax:
● non-nullable - Int, String, User
● nullable - Int?, String?, User?
● User? is super class of User as it can hold null additionally.

Type Hierarchy
Any
StringInt User

Type Hierarchy
Any
StringInt User
Nothing

Type Hierarchy
Any
StringInt User
Nothing
Any?

Type Hierarchy
Any
StringInt User
Nothing
Any?
Int?

Type Hierarchy
Any
StringInt User
Nothing
Any?
String?Int?

Type Hierarchy
Any
StringInt User
Nothing
Any?
String?Int? User?

Type Hierarchy
Any
StringInt User
Nothing
Any?
String?Int? User?
Nothing?

Examples - Nullable Types
var nullableName: String = null

Compilation Error: Can't assign null to a nun-null String

var nullableName: String? = null

Compiles fine

var name: String = "BangaloreJUG"

Type - Non Nullable

Type - Non Nullable Value should not be null

nullableName = name

nullableName = name
Compiles fine: String is sub-class of String?

nullableName = name
name = nullableName

nullableName = name
name = nullableName
Compilation Error: You know why

Let’s return multiple values from a function

var email: String,
var phone: String)

var email: String,
var phone: String)
fun getUser() = User("BangaloreJUG",
"bangalorejug@gmail.com",
"0000000000")

var email: String,
var phone: String)
val (name, email, phone) =
User("Chandra Sekhar Nayak",
"chansek@live.com",
"8792629767")
println("Name is - $name")
println("Email is - $email")
println("Phone is - $phone")fun getUser() = User("BangaloreJUG",
"0000000000")

var email: String,
var phone: String)
"chansek@live.com",
"8792629767")
"0000000000")
val (group, _, contact) = getUser()
println("Meetup Group name - $group")
println("Contact number - $contact")

var email: String,
var phone: String)
"chansek@live.com",
"8792629767")
"0000000000")
val (group, _, contact) = getUser()
println("Meetup Group name - $group")
println("Contact number - $contact")for ((key, value) in map) {
// do something with key and value
}

The world of .. operator
if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}

if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}
for (i in 1..4) print(i) // "1234"

if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}
for (i in 1..4) print(i) // "1234"
for (i in 4..1) print(i) // No Output
for (i in 4 downTo 1)
print(i) // "4321"

if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}
for (i in 1..4 step 2) print(i) // "13"
for (i in 1..4) print(i) // "1234"
print(i) // "4321"

if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}
for (i in 1..4) print(i) // "1234"
print(i) // "4321"
for (i in 4 downTo 1 step 2)
print(i) // "42"

if (i in 1..10) { // 1 <= i && i <= 10
println(i)
}
for (i in 1..4) print(i) // "1234"
// i in [1, 10), 10 is excluded
for (i in 1 until 10) {
println(i)
}
print(i) // "4321"
for (i in 4 downTo 1 step 2)
print(i) // "42"

Unary Operations
data class Point(val x: Int, val y: Int)

Unary Operations
operator fun Point.unaryMinus() = Point(-x, -y)

Unary Operations
fun main(args: Array<String>) {
val point = Point(10, 20)
println(-point) // prints "(-10, -20)"
}

Unary Operations
• 3 operators are supported.
}

Unary Operations
• Function names should not be changed.
}

Unary Operations
• Like this there are some other functions for different operators.
}

Unary Operations
• Like this there are some other functions for different operators.
}
Expression Function
+a a.unaryPlus()
-a a.unaryMinus()
!a a.not()

Increment and Decrement Operations

Increment and Decrement Operations
Expression Function
a++ a.inc()
a— a.dec()

Expression Function
a++ a.inc()
a— a.dec() Expression Function
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.rem(b)
a..b a.rangeTo(b)
Binary Operations

Expression Function
a++ a.inc()
a— a.dec()
Expression Function
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.rem(b)
a..b a.rangeTo(b)
Binary Operations

Expression Function
a++ a.inc()
a— a.dec()
Expression Function
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.rem(b)
a..b a.rangeTo(b)
Expression Function
a in b b.contains(a)
a !in b !b.contains(a)
‘in’ Operator

Expression Function
a++ a.inc()
a— a.dec()
Expression Function
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.rem(b)
a..b a.rangeTo(b)
Expression Function
Expression Function
a[i] a.get(i)
a[i, j] a.get(i, j)
a[i1, i2, .., in] a.get(i1, i2, .., in)
a[i] = b a.set(i, b)
a[i, j] = b a.set(i, j, b)
a[i1, i2, .., in] = b a.set(i1, i2, .., in, b)
Indexed Access Operator

Expression Function
a++ a.inc()
a— a.dec()
Expression Function
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.rem(b)
a..b a.rangeTo(b)
Expression Function
Expression Function
a[i] a.get(i)
a[i, j] a.get(i, j)
a[i1, i2, .., in] a.get(i1, i2, .., in)
a[i] = b a.set(i, b)
a[i, j] = b a.set(i, j, b)
a[i1, i2, .., in] = b a.set(i1, i2, .., in, b)
Expression Function
a() a.invoke()
a(i) a.invoke(i)
a(i, j) a.invoke(i, j)
Invoke Operator

Extending an existing class
● The most powerful feature of Kotlin

● No utility class is required

● IDE can auto suggest

● IDE can auto suggest
● Accidentally multiple utility function for same doesn’t get
created

Let’s extend the functionality of a library class

fun ArrayList<String>.swap(index1: Int, index2: Int) {
val tmp = this[index1]
this[index1] = this[index2]
this[index2] = tmp
}

fun ArrayList<String>.swap(index1: Int, index2: Int) {
val tmp = this[index1]
this[index1] = this[index2]
this[index2] = tmp
}
val list = arrayListOf("BangaloreJUG", "BlrKotlin", "BlrDroid")
list.swap(0, 1)
print(list)
}

Inline Functions
var value = 0
value = a
func()
}
fun operate(a: Int, func: () -> Unit) {

Inline Functions
var value = 0
value = a
func()
}
assignAndOperate(2) {
value *= 5
}
println(value)
operate(2) {
value *= 10
}
println(value)
}
fun operate(a: Int, func: () -> Unit) {

Inline Functions
var value = 0
value = a
func()
}
value *= 5
}
println(value)
operate(2) {
value *= 10
}
println(value)
}
fun operate(a: Int, func: () -> Unit) {inline

Inline Functions
var value = 0
value = a
func()
}
value *= 5
}
println(value)
operate(2) {
value *= 10
}
println(value)
}
fun operate(a: Int, func: () -> Unit) {inline
inline tells compiler to copy the function body
to each calling place.

Infix Functions
class Couple(private val first: String, private val second: String)

Infix Functions
fun getOldCouples() = arrayListOf(
Couple("Virat", “Anushka"),
Couple("Rekha", “Amitabh")
)

Infix Functions
)
infix fun String.loves(that: String) = Couple(this, that)

Infix Functions
)
fun getModernCouples() = arrayListOf(
"Virat" loves "Anushka",
"Rekha" loves "Amitabh"
)

Infix Functions
)
fun getModernCouples() = arrayListOf(
"Virat" loves "Anushka",
"Rekha" loves "Amitabh"
)
val languages = mapOf(1 to "Java", 2 to "Kotlin", 3 to "Scala")

Calling Java from Kotlin
public class Student {
private String rollNo;
public void setName(String name) {
this.name = name;
}
public String getRollNo() { return rollNo; }
public void setRollNo(String rollNo) {
this.rollNo = rollNo;
}
}

this.name = name;
}
}
}
val student = Student()
student.name = "Rahim"
student.rollNo = "R1"
val name = student.name
val rollNo = student.rollNo
}

this.name = name;
}
}
}
}
same as student.setName(“Rahim”)

this.name = name;
}
}
}
}
same as student.getRollNo()

Calling Kotlin from Java
class Meetup {
var name: String = ""
var location: String = ""
}

class Meetup {
}
public class Main {
public static void main(String... args) {
Meetup meetup = new Meetup();
meetup.setName("BangaloreJUG");
meetup.setLocation("Oracle");
System.out.println(meetup.getName());
System.out.println(meetup.getLocation());
}
}

class Meetup {
}
public class Main {
}
}
same as meetup.name = “Rahim”

class Meetup {
}
public class Main {
}
}
same as meetup.location

A small example
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
}

A small example
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
}
launch new coroutine in background and continue

A small example
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
}
non-blocking delay for 1 second (default time unit is ms)

A small example
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
}
print after delay

A small example
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
}
main thread continues while coroutine is delayed

Thank You
Join BlrKotlin for continuing your journey in Kotlin
@iChanSek www.chansek.com
meetup.com/blrkotlin blrkotlin.herokuapp.com

BangaloreJUG introduction to kotlin

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