CodeBlanks Logo Icon CodeBlanks
Login Register

Default parameters

Learn to define parameters with default values.

Default parameters: default values

You can give a parameter a default value: fun greet(name: String, msg: String = "Hi"). If the caller omits it, the default is used; if provided, it overrides.

fun greet(name: String, msg: String = "Hi") {
    println("$msg $name")
}
greet("Ava")          // Hi Ava
greet("Ava", "Hello") // Hello Ava

Default parameters let one definition support many usage forms; they reduce the need for overloads.

Order of default parameters

Default parameters usually sit at the end of the parameter list. This lets the caller pass the leading required parameters by position and omit the rest.

fun order(item: String, qty: Int = 1, gift: Boolean = false)
order("book")           // qty=1, gift=false
order("book", 3)        // qty=3, gift=false
order("book", 3, true)  // qty=3, gift=true

If a non-default parameter comes after a default one, the caller must use a named argument to skip the default one.

Practice Define greet with a default parameter

Define a fun greet(name: String, msg: String = "Hello") whose body is println("$msg $name"). From main call greet("Ava").

Starter code

Main.kt
fun main() {
    // Call greet with "Ava" (msg uses its default)
}

// Define greet: msg parameter defaults to "Hello"

Sample solution

Main.kt
fun main() {
    greet("Ava")
}

fun greet(name: String, msg: String = "Hello") {
    println("$msg $name")
}

Expected output

Hello Ava

Questions and answers

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

1 Fill in the blank: default value

Question 
fun greet(name: String, msg: String ____ "Hello")
Answer 
fun greet(name: String, msg: String = "Hello")

Explanation: msg: String = "Hello" assigns a default value.

2 Match call form to outcome

Term Meaning
msg: String = "Hi" Parameter with default
name: String Required parameter
greet("Ava") Default is used
greet("Ava", "Hi") Default is overridden

3 fun greet(name: String, msg: String = "Merhaba"); what does greet("Ayşe") print?

  • Merhaba Ava Correct answer
  • Ava
  • Throws an exception
  • Hi Ava

Explanation: Since msg is not given, the default "Merhaba" is used.

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