Basics of Kotlin for Android Development


Basics of Kotlin for Android Development

written on 2021-01-26 by SAURABH JADHAV | tech

Hey So we will start with Iconic Hello world !

Hello World

kotlin fun main(){ println("Hello world") } Out: Hello world

So is as simple as that, Now println() is used for next line.

```kotlin print("Hello") //next print will continue prining withought next line print("saurabh")

Out: Hellosaurabh

//So with println next line will be used println("Hello") println("Saurabh")

Out: Hello Saurabh ```


```kotlin fun mm(){ //fun is used to declare a function println(2)

} ```

For calling function Of course we have to define in main()


```kotlin fun mm( ){ println(2)

} fun main() { mm() }

Out: 2 ```

Passing Arguments

```kotlin fun mm( x: String){ println(x+x+2) //yes concatenation works too ! }

fun main() { mm("Hello") //It will print--> HelloHello2
} ```

Defining return type

```kotlin fun main() { print(add(2,3))


fun add(a:Int,b:Int):Int{ //here we have set return type as Int //return type is preceeded by ':' return a+b }


5 ```

Single Line Fun()

```kotlin fun main() { print(add(2,3))


fun add(a:Int,b:Int):Int=a+b //isnt it good? Out: 5 ```

Default Parameters

```kotlin fun main() { greetings("Good morning") greetings() //default will be used }

fun greetings(greet: String="olllala"){ //we assigne "Olalla" for default if no args is passed println("Hello $greet") }

Out: Hello Good morning Hello olllala //default is used ```


kotlin var number = 42 var message = "Hello"

So here number is of type Int and message is of String

Type is automatically detect by type of data we put into variable.

But in var number , we cant put String or other type of datatype in future.

Read Only Variables

kotlin val message = "Hello" val number = 42 //The value of variable define with val cant be reassigned


kotlin const val x = 2 //note u cant define constant inside class decalration

Specifying data Type explicitly

kotlin val x:String="Hello Saurabh" //by using colon and following with datatype

It is useful when you are using multiple classes.

Using variable in Print

Use $ sign here.

kotlin fun main() { var a="Saurabh" println("Hello $a") } Out: Hello Saurabh


Use curly brackets for operations.

kotlin fun main() { var a=10 var b=20 println("Hello ${a+b}") } Out: Hello 30

Null Safety

```kotlin var neverNull: String = "This can't be null"

neverNull = null

var nullable: String? = "You can keep a null here"

nullable = null

You have to add ? so it can store null.



if else is normal like other languages .

kotlin fun main() { a=10 if(a<12) { println("a is smaller than 10") } else{ print("Olllala") } }

For elif like python - use Else if

If you wrote block in one line then no need to use curly brackets but if used then its good.


kotlin val result = if (condition) trueBody else falseBody Eg: fun main() { var op= if(2<10) print("Yes") else print("Nonsense") println(op) }

When -its like Switch case

```kotlin var x="Saurabh" when(x){

        print("Its saurabh")
        print("its Hello")

Its saurabh


So you got? Just add -> this symbol “One hyphen followed by arrow”

while else is like default in Switch case.



```kotlin var strings= listOf("abc","def","ghj") //you can pass combo of number and strings also print(strings)

Out: [abc, def, ghj] ```

If you want to pass data of only certain type then explicity define it


```kotlin val names= mutableListOf("hello",1) print(names)

Out: //It will give error //Kotlin: The integer literal does not conform to the expected type String val names= mutableListOf("hello",1) print(names)

Out: [hello, 1] ```


Its like an dictionary in python

kotlin var map= mapOf("a" to 1,"b" to 2,"c" to 3 ) print(map) Out: {a=1, b=2, c=3}

In map to is in internal function which creates pair of both.


```kotlin var set= setOf("abc","def","ghj") print(set)

Out: [abc, def, ghj] ```


IN kotlin this collection we define above are by default immutable

if we want to change data we can’t so we can define by saying mutableListOf()

So it will be mutable list.

Control flow

For loop

kotlin val name= arrayOf("av","def","sd") for(n in name){ println(n) } Out: av def sd

Loops are like Python…or like for each like java

While and Do-while works normally like other languages


kotlin for (i in 0..3)//it is like again python but it will print 3 also { println(i) } Out: 0 1 2 3

Char Support:

kotlin for (c in 'a'..'d') { println(c) } Out: a b c d

Other Option for ranges:


```kotlin for (i in 0 until 2) { println(i) }

Out: 0 1 ```


```kotlin for (i in 0..5 step 2)//It will jump or skip 2 iterations or values { println(i) }

Out: 0 2 4 ```