Elvis operator

Learn the Elvis operator with ?: and null safety.

The Elvis operator

The Elvis operator ?: returns the value itself when it is not null, otherwise a default value. Its name comes from the ?: sign resembling a smiley (Elvis Presley).

In val name = input ?: "Guest", if input is null, name becomes "Guest"; otherwise it becomes input itself.

val input: String? = null
val name = input ?: "Guest"
println(name)  // Guest

Exercise Try Elvis

At the top level, declare val input: String? = null. Inside fun main(), declare val name = input ?: "Guest" and print with println(name).

Show example solution

val input: String? = null

fun main() {
    val name = input ?: "Guest"
    println(name)
}

Null safety

In Kotlin a type cannot be null by default; String cannot be null but String? can. The Elvis operator ?: handles nullable values safely.

There is also the !! operator; but it throws NullPointerException if the value is null. Elvis is safer; it gives a default value and prevents the program from crashing.

Test yourself

Elvis operator: fill in the missing part

val name = input ____ "Guest"

Show answer

val name = input ?: "Guest"

When is the Elvis operator used?
- In class definitions
- Only for arithmetic
- In loops
- To give defaults to null values
Show answer

To give defaults to null values — ?: gives a default in null cases.
Elvis operator: match the terms

?:

Elvis
&&

And
||

Or
!

Not

Next lesson: Summary - Operators

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