Kotlin: nullable types

By default, kotlin reference types (Int, Float, Double, String etc.,) do not take null values. Kotlin introduced this feature to avoid null pointer exceptions.

Test.kt

fun main(args: Array<String>) {
 var name : String = "Krishna"
 
 name = null
}

When you try to compile above program, kotlin throws below error.

ERROR: Null can not be a value of a non-null type String (6, 9)

How can I define a variable that take null value?

By using nullable types, you can define a variable that takes null values. Append the ‘?’ to the reference type to take null values.

Type	Nullable type
Int	Int?
String	String?
Double	Double?
Person	Person?

Ex

 var id: Int? = 1
 var name: String? = "Krishna"
 var salary: Double? = 123.456
 var person: Person? = Person("Krishna")

 id = null
 name = null
 salary = null
 person = null

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