What does ?: do in Kotlin? (Elvis Operator)

Question

I can\'t figure out what ?: does in for example this case

val list = mutableList ?: mutableListOf() 

and why can it be modifi

Answer 1

Simply we can say that, you have two hands. You want to know, is your left hand working right now?. If left hand not working, return empty else busy

Example for Java:

private int a;
if(a != null){
    println("a is not null, Value is: "+a)
}
else{
    println("a is null")
}

Example for Kotlin:

val a : Int = 5
val l : Int = if (a != null) a.length else "a is null"