CodeBlanks Logo Icon CodeBlanks
Login Register

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

Practice Try Elvis

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

Sample solution

Main.kt
val input: String? = null

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

Expected output

Guest

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.

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Elvis operator: fill in the missing part

Question 
val name = input ____ "Guest"
Answer 
val name = input ?: "Guest"

Explanation: With ?: you give a default for the null case.

2 When is the Elvis operator used?

  • In class definitions
  • Only for arithmetic
  • In loops
  • To give defaults to null values Correct answer

Explanation: ?: gives a default in null cases.

3 Elvis operator: match the terms

Term Meaning
?: Elvis
&& And
|| Or
! Not

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together