Kotlin Basic Tutorial-Null value security

NULL security

An important feature of the Kotlin system is its commitment to eliminate null references. Avoid any NPE (nullpointerexception) exceptions.

Defining a variable that is allowed to be empty in Kotlin is not allowed to be defined in an empty way.

var a:string = "ABC"//Cannot be an empty

var b:string? = "ABC"//Can be empty
b.length//may error
//second one more than the first one '? '

Null value Check

Val L = if (b! = null) b.length () else-1

Secure call

B?. Length ()

If B is empty, returns without calling the length () Elvis operator

?:

Val L = b.length ()?: 1

If B is empty, then l=-1.

Check function parameters generally write this:

Fun foo (node:node): String? {
  val parent = Node.getparent ()?: return null
  val name = Node.getname ()?: Throw IllegalArgumentException ("name E xpected ")

  //...
}

!! Operator

Val b:string? = null
val L = b!!. Length

Safe conversion

Val aint:int? = A as? Int