Kotlin Boolean

In Kotlin, Boolean is a fundamental data type representing a logical entity that can possess one of exactly two values: true or false. On the JVM, a non-nullable Boolean is compiled to a primitive boolean to optimize memory and performance, while a nullable Boolean? is boxed as a java.lang.Boolean object reference. To maintain primitive memory optimization for arrays on the JVM, Kotlin provides the BooleanArray type, which compiles to a primitive boolean[]. In contrast, using a standard Array<Boolean> results in an array of boxed objects (Boolean[]).

Declaration and Instantiation

Boolean variables and arrays can be declared explicitly or inferred by the compiler.

val isEnabled: Boolean = true
val isVisible = false // Type inferred as Boolean
val isOptional: Boolean? = null // Boxed, nullable Boolean

val primitiveArray = BooleanArray(3) // Compiles to boolean[]
val boxedArray = arrayOf<Boolean>(true, false) // Compiles to Boolean[]

Logical Operators

Kotlin provides standard logical operators for Boolean types. The conjunction and disjunction operators utilize short-circuit evaluation, meaning the right-hand operand is only evaluated if the left-hand operand does not definitively determine the outcome.

|| (Logical OR): Returns true if at least one operand is true. Short-circuits if the left operand is true.
&& (Logical AND): Returns true if both operands are true. Short-circuits if the left operand is false.
! (Logical NOT): A unary operator that inverts the boolean value.

val a = true
val b = false

val conjunction = a && b // Evaluates to false
val disjunction = a || b // Evaluates to true
val negation = !a        // Evaluates to false

Infix Functions

In addition to standard operators, Kotlin provides infix functions for boolean arithmetic. Unlike && and ||, these infix functions do not short-circuit; both operands are always evaluated.

and: Performs a logical AND operation.
or: Performs a logical OR operation.
xor: Performs a logical exclusive OR operation. Returns true strictly when the operands evaluate to different values.

val x = true
val y = false

val resultAnd = x and y // Evaluates to false
val resultOr = x or y   // Evaluates to true
val resultXor = x xor y // Evaluates to true

Nullability and Equality

When working with a nullable Boolean?, standard logical operators (&&, ||, !) cannot be used directly without prior null-checking or unwrapping. However, structural equality operators (==, !=) are null-safe.

val flag: Boolean? = null

// Structural equality safely handles the null reference
val isStrictlyTrue = (flag == true)   // Evaluates to false
val isStrictlyFalse = (flag == false) // Evaluates to false

String Conversion

The Kotlin String API provides extension functions to parse string values into Boolean types. These functions offer varying levels of strictness regarding case sensitivity and format validation.

toBoolean(): Case-insensitive and lenient. Returns true if the string is equal to "true" (ignoring case), and safely returns false for any other string, including invalid formats.
toBooleanStrict(): Strictly case-sensitive. Returns true for "true" and false for "false", but throws an IllegalArgumentException for any other value.
toBooleanStrictOrNull(): Strictly case-sensitive, but returns null instead of throwing an exception for invalid formats.

// Lenient parsing
val lenientTrue = "True".toBoolean()            // Returns true
val lenientFalse = "random".toBoolean()         // Returns false

// Strict parsing
val strictTrue = "true".toBooleanStrict()       // Returns true
// val error = "True".toBooleanStrict()         // Throws IllegalArgumentException
val safeParse = "1".toBooleanStrictOrNull()     // Returns null

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Declaration and Instantiation

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Nullability and Equality

String Conversion

​Declaration and Instantiation

​Logical Operators

​Infix Functions

​Nullability and Equality

​String Conversion

Declaration and Instantiation

Logical Operators

Infix Functions

Nullability and Equality

String Conversion