Kotlin — Data Types

Basic types

Type	Description
Boolean	true or false
Byte	8-bit signed
Short	16-bit signed
Int	32-bit signed
Long	64-bit signed
Float	32-bit float
Double	64-bit float
Char	Unicode character
String	UTF-8 text

Number types

fun main() {
    val b: Byte = 127
    val s: Short = 32000
    val i: Int = 2147483647
    val l: Long = 9223372036854775807L
    val f: Float = 3.14f
    val d: Double = 3.141592653589793

    println("$b, $s, $i, $l, $f, $d")
}

Strings

val s = "Hello"
val raw = """Raw string
with newlines"""
val interpolated = "Length: ${s.length}"

println(interpolated) // Length: 5

Collections

// List (immutable)
val nums = listOf(1, 2, 3, 4, 5)

// MutableList
val mutable = mutableListOf(1, 2, 3)
mutable.add(4)

// Map
val map = mapOf("Alice" to 30, "Bob" to 25)

// Set
val set = setOf(1, 2, 3, 2, 1) // [1, 2, 3]

// Empty collections
val emptyList = emptyList<String>()
val emptyMap = emptyMap<String, Int>()

Data classes

data class Person(val name: String, val age: Int)

fun main() {
    val p1 = Person("Alice", 30)
    val p2 = Person("Alice", 30)

    println(p1)            // Person(name=Alice, age=30)
    println(p1 == p2)      // true (structural equality)
    println(p1.name)       // Alice

    // Copy
    val p3 = p1.copy(age = 31)
    println(p3)            // Person(name=Alice, age=31)
}

Type aliases

typealias UserId = String
typealias UserMap = Map<UserId, User>

fun main() {
    val id: UserId = "user-123"
    println(id)
}

Mini Practice

Write Kotlin code that:

1. Creates variables of each primitive type
2. Uses a data class with destructuring
3. Creates and manipulates a MutableList
4. Demonstrates a type alias

Up Next

In the next lesson, you'll learn about Operators — arithmetic and logical operations in Kotlin.