val and var

Learn to declare variables with val (immutable) and var (mutable).

val and var

In Kotlin you declare two kinds of variables. A variable declared with val (value) is assigned once and cannot be changed afterwards; this is called immutable. A variable declared with var (variable) can be reassigned later; this is called mutable.

Kotlin recommends using val by default and switching to var only when the value really needs to change.

val pi = 3.14    // immutable
var counter = 0   // mutable
counter = counter + 1

Exercise Declare a counter

Write a fun main(). Declare var counter = 0. Then increment with counter = counter + 1 and print with println(counter).

Show example solution

fun main() {
    var counter = 0
    counter = counter + 1
    println(counter)
}

When to use val?

The Kotlin community recommends using val by default. Variables declared with val are safer; since they don't change after assignment, code behavior is more predictable.

You switch to var only for loop counters, fresh user input, or running totals. This habit is especially valuable in concurrent code.

Test yourself

Which cannot be reassigned?
- const
- var
- val
- lateinit
Show answer

val — A variable declared with val is assigned once.

val and var: fill in the missing part

____ counter = 0
counter = counter + 1

Show answer

var counter = 0
counter = counter + 1

Which statement is true?
- val is mutable, var is immutable
- val is immutable, var is mutable
- Both are immutable
- Both are mutable
Show answer

val is immutable, var is mutable — val is immutable, var is mutable.

Next lesson: Type inference

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies