Writing Null-Safe Code (the ?: Elvis operator)

In this lesson you will learn null-safe code in Kotlin with the Elvis operator, and how to avoid errors when a value has not been set. This is for anyone searching for "Kotlin Elvis operator how to use".

?: (the Elvis operator) uses the right-hand value only when the left is null. Taking null safety seriously at the language level is one of Kotlin's defining features.

The sample code writes address ?: "No address set" against a variable declared as val address: String? = null, showing a replacement string when there is no value. Adding ? after the type, as in String?, states explicitly that the type allows null.

A common stumbling block for beginners is that a variable declared without ? cannot hold null at all. Kotlin checks for the possibility of null at compile time, so nullable and non-nullable have to be distinguished strictly through the type.

In real-world development this mechanism makes it much easier to write code that does not throw NullPointerException - one of the big reasons Kotlin is so well regarded.