kotlin Data Types

Numbers

Kotlin provides several built-in types to represent numbers, categorized into integers and floating-point numbers. Unlike Java, there are no implicit widening conversions for numbers (e.g., you cannot assign an Int to a Long variable without an explicit conversion).

val inferedInt = 10 // Inferred as Int
val inferedLong = 10000000000 // Inferred as Long because it's too big for Int
val explicitLong = 10L // Explicitly defined as Long

val inferedInt = 10 // Inferred as Int
val inferedLong = 10000000000 // Inferred as Long because it's too big for Int
val explicitLong = 10L // Explicitly defined as Long

Integer Types

These types represent whole numbers without decimals.

Floating-Point Types

These types represent numbers with decimal points. Kotlin adheres to the IEEE 754 standard for floating-point numbers.

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Booleans

The Boolean type represents logical values and has only two possible states: true and false. This type is fundamental for control flow structures like if statements and loops.

val isKotlinFun: Boolean = true
val isFishTasty = false // Type inference makes it a Boolean

if (isKotlinFun) {
    println("Yes, it is!")
}

val isKotlinFun: Boolean = true
val isFishTasty = false // Type inference makes it a Boolean

if (isKotlinFun) {
    println("Yes, it is!")
}

Characters

The Char type represents a single 16-bit Unicode character. Character literals are enclosed in single quotes, like 'A' or '1'.

val letter: Char = 'K'
val digit = '7' // Inferred as Char
// val notAChar = 'KO' // Error: too many characters

val letter: Char = 'K'
val digit = '7' // Inferred as Char
// val notAChar = 'KO' // Error: too many characters

Crucially, in Kotlin, Char is NOT a number type. You cannot directly assign a character to an integer variable (unlike in Java). You must use explicit conversion functions like .toInt() to get its ASCII/Unicode value.

val c = 'A'
// val i: Int = c // Error: Type mismatch
val code: Int = c.toInt() // Works, code will be 65

val c = 'A'
// val i: Int = c // Error: Type mismatch
val code: Int = c.toInt() // Works, code will be 65

Strings

The String type represents an immutable sequence of characters. String literals are enclosed in double quotes, like "Hello, KtDevLog!".

val greeting: String = "Welcome!"
val name = "Sharif" // Inferred as String

val greeting: String = "Welcome!"
val name = "Sharif" // Inferred as String

Arrays

Arrays in Kotlin are represented by the Array class. They are invariant, meaning Array<String> is not a subtype of Array<Any>. You can create arrays using functions like arrayOf(), arrayOfNulls(), or the Array constructor.

val numbers = arrayOf(1, 2, 3, 4, 5) // Inferred as Array<Int>
val names: Array<String> = arrayOf("Sharif", "Mia", "KtDevLog")

val numbers = arrayOf(1, 2, 3, 4, 5) // Inferred as Array<Int>
val names: Array<String> = arrayOf("Sharif", "Mia", "KtDevLog")