#Booleans

Last modified: 05 May 2026

The Boolean type represents logical values: true and false.

Use Boolean values in functions that answer yes-or-no questions, and in the while, if, and when conditions.

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#Declare a Boolean variable

To declare a Boolean variable, assign it true or false. You can specify the Boolean type explicitly or let Kotlin infer it from the value:

kotlincopyval isTrue: Boolean = true
val isFalse = false // Kotlin infers Boolean

If a value can be null, use Boolean?:

kotlincopyval isEnabled: Boolean? = null

Note: You cannot assign an integer value to a Boolean variable. In Kotlin, 0 and 1 are not Boolean values.

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#Produce Boolean values

You can use comparison expressions and functions to produce Boolean values:

kotlincopyval number = 10
val isPositive = number > 0
println(isPositive) // true

val language = "Kotlin"
val isEmpty = language.isEmpty()
println(isEmpty) // false

You can use the results in conditions and other expressions as well:

kotlincopyval number = 10
val isPositive = number > 0 // true

if (isPositive) {
    println("The number is positive.")
}

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#Boolean operations

Kotlin provides operators and infix functions for working with Boolean values. You can use them to invert a Boolean value or combine multiple Boolean values into a single result.

#Negation (NOT)

The NOT operator inverts a Boolean value. To use NOT, place the ! operator before a Boolean value:

kotlincopyval isOn = true
val isOff = !isOn // isOff is false

#Logical AND

The AND operator returns true only if both operands are true. To use logical AND, place the && operator between operands:

kotlincopyval a = false && false // false
val b = false && true // false
val c = true && false // false
val d = true && true  // true

If the first operand is false, the && operator skips the second operand. To evaluate both operands, use the and infix function instead.

#Logical OR

The OR operator returns true if at least one operand is true. To use logical OR, place the || operator between operands:

kotlincopyval a = false || false // false
val b = false || true  // true
val c = true || false  // true
val d = true || true   // true

If the first operand is true, the || operator skips the second operand. To evaluate both operands, use the or infix function instead.

#Exclusive OR (XOR)

The exclusive OR (XOR) operation returns true if the operands have different values. To use XOR, write xor between operands:

kotlincopyval a = false xor false // false
val b = false xor true  // true
val c = true xor false  // true
val d = true xor true   // false

xor is an infix function, not an operator.

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#Operator precedence

If an expression contains multiple logical operations and no parentheses to specify the evaluation order, Kotlin applies precedence rules.

In the following example, the compiler evaluates && before ||:

kotlincopyval result = true || false && false
println(result) // true

To make evaluation order explicit, use parentheses:

kotlincopyval result = (true || false) && false
println(result) // false

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#Boolean in conditions

if, when, and while evaluate Boolean expressions to direct program flow.

#if expressions

kotlincopyval number = 4
val isEven = number % 2 == 0

// Condition already has the Boolean type
// You do not need to compare it to true or false
if (isEven) {
    println("The number is even.")
} else {
    println("The number is odd.")
}

#when expressions

kotlincopyval number = 3

when {
    number > 0 -> println("The number is positive.")
    number < 0 -> println("The number is negative.")
    else -> println("The number is zero.")
}

#while loops

kotlincopyvar isCalculating = true

while (isCalculating) {
    println("Calculating...")
    isCalculating = false
}