Kotlin if Expression

In this article, you will learn to use if expression in Kotlin with the help of examples.

Traditional Usage of if...else

The syntax of if...else is:

if (testExpression) {
   // codes to run if testExpression is true
}
else {
  // codes to run if testExpression is false
}

if executes a certain section of code if the testExpression is evaluated to true. It can have optional else clause. Codes inside else clause are executed if the testExpression is false.


Example: Traditional Usage of if...else

fun main(args: Array<String>) {

    val number = -10

    if (number > 0) {
        print("Positive number")
    } else {
        print("Negative number")
    }
}

When you run the program, the output will be:

Negative number

Kotlin if expression

Unlike Java (and other many programming languages), if can be used an expression in Kotlin; it returns a value. Recommended Reading: Kotlin expression


Here is an example:

Example: Kotin if expression


fun main(args: Array<String>) {

    val number = -10

    val result = if (number > 0) {
        "Positive number"
    } else {
        "Negative number"
    }

    println(result)
}

When you run the program, the output will be:

Negative number

The else branch is mandatory when using if as an expression.


The curly braces are optional if the body of if has only one statement. For example,

fun main(args: Array<String>) {
    val number = -10
    val result = if (number > 0) "Positive number" else "Negative number"
    println(result)
}

This is similar to ternary operator in Java. Hence, there is no ternary operator in Kotlin.


Example: if block With Multiple Expressions

If the block of if branch contains more than one expression, the last expression is returned as the value of the block.

fun main(args: Array<String>) {

    val a = -9
    val b = -11

    val max = if (a > b) {
        println("$a is larger than $b.")
        println("max variable holds value of a.")
        a
    } else {
        println("$b is larger than $a.")
        println("max variable holds value of b.")
        b
    }
    println("max = $max")
}

When you run the program, the output will be:

-9 is larger than -11.
max variable holds value of a.
max = -9

Recommended Reading: Kotlin when Statement


Kotlin if..else..if Ladder

You can return a block of code among many blocks in Kotlin using if..else...if ladder.


Example: if...else...if Ladder

fun main(args: Array<String>) {

    val number = 0

    val result = if (number > 0)
        "positive number"
    else if (number < 0)
        "negative number"
    else 
        "zero"
    
    println("number is $result")
}

This program checks whether number is positive number, negative number, or zero.


Kotlin Nested if Expression

An if expression can be inside the block of another if expression known as nested if expression.


Example: Nested if Expression

This program computes the largest number among three numbers.

fun main(args: Array<String>) {

    val n1 = 3
    val n2 = 5
    val n3 = -2

    val max = if (n1 > n2) {
        if (n1 > n3)
            n1
        else
            n3
    } else {
        if (n2 > n3)
            n2
        else
            n3
    }

    println("max = $max")
}

When you run the program, the output will be:

max = 5