Kotlin Tutorial · Kotlin Basics · Lesson 5 of 31

Kotlin Data Types

Numbers, booleans, characters and strings, type conversion, and how Kotlin maps them to the JVM.

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Basic types

Type	Example	Notes
`Int`, `Long`	`42`, `3_000_000_000L`	32-bit and 64-bit integers
`Double`, `Float`	`3.14`, `2.5f`	floating point
`Boolean`	`true`
`Char`	`'K'`	a single character
`String`	`"Kotlin"`	immutable text

Everything is an object (you can call 42.toString()), but the compiler uses fast JVM primitives where it can.

Basic types

fun main() {
    val users = 42
    val population = 3_000_000_000L
    val ratio = 0.75
    val active = true
    val grade = 'A'
    println("$users ${users::class.simpleName}")
    println("$population ${population::class.simpleName}")
    println("$ratio $active $grade")
    println(Int.MAX_VALUE)
}

Output

42 Int
3000000000 Long
0.75 true A
2147483647

Run this on your computer — see “Get Started” for setup.

No implicit conversions

Kotlin never converts numbers silently: an Int isn't assigned to a Long without toLong(). Integer division truncates; use a Double to get a fraction.

Conversions and arithmetic

fun main() {
    val items = 7
    val boxes = 2
    println(items / boxes)               // integer division
    println(items % boxes)               // remainder
    println(items.toDouble() / boxes)    // convert first
    val total: Long = items.toLong() * 1_000_000_000
    println(total)
    println("42".toInt() + 1)
    println("abc".toIntOrNull())
}

Output

Run this on your computer — see “Get Started” for setup.

Test yourself

What does 7 / 2 evaluate to when both are Int?

3.5
3
4
A compile error

Show answer

Answer: 3

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