Null Safety , Lazy Keyword and LateInit Keyword

Null Safety :-

Safe call  ( ? )    use it if you don't mind getting null values

Not Null Insertion ( !! )  use if you are sure that value is not null otherwise throw Nullpointer Exception

Elvis ( ?: )  goes with function when values is not null, otherwise decided value

Safe call with let ( ?.Let { .. } ) execute the block only value is not null

In Android, we mostly use safe call and not null insertion.

eg :-

fun main(args:Array<String>) {

    var s: String? = null                //safe call

    println("The lenght of name is ${s?.length}")

    s?.let {                            //safe call with let

        println("The length of name is ${s.length}")

    }

    var len = {            // same below code as elvis

        if (s != null) 

            s.length

        else

            -1

    }

    var len1 = s?.length?:-1           //elvis

    println("The length of name is ${len1}")

    println("the length of name is ${s!!.length}")   //not null insertion

}

Lazy keyword :-

prevent unnecessary initialization of object.

can be var/val , null/not null and thread safe

 val pi: Float by lazy {

    3.14f

}

fun main (args:Array<String>)

{

 println("some initial code..")

 var a =pi*3*3

 var b = pi*a*a

 println("some more code...")

}

LateInit Keyword :-

Initialize the variable later, when used otherthrow uninitializedpropertyAccess Exception.

Allowed with only not null values

promise to compiler that value will initialize in Future 

** Mainly Helpful in Android Programming

fun main(args:Array<String>)

{

    var a = animal();

//    a.name = "Cat"

//println("name : ${a.name}")

    a.check()

}

class animal

{

    lateinit var name:String   //use of late init

    fun check()

    {

        name = "Monkey"

        println("name in function : ${name}")

    }

}