Hey, What About ?

If you read through Kotlin code, you will see variables declared with questions for types:

var something : Boolean? = null

println("something was: $something")

something = true

println("something is now: $something")

Kotlin has many features that are not seen very often in other programming languages. One of the most important of these features is how Kotlin handles null values. Boolean is a type that is either true or false, while Boolean? is a type that is either true, false, or null.

We will explore “nullability” in much greater detail later in the book. For now, take it on faith that we can assign null to a variable whose type ends in ?, and we cannot assign null to a variable whose type does not end in ?. So, where you see ? in types, watch out for null values.