Kotlinの基本型：Int、Double、Boolean、Char

Kotlinの型システム

整数型

val age: Int = 25
val population: Long = 8_000_000_000L
val score: Short = 100
val flags: Byte = 0b00001111

浮動小数点型

val pi: Double = 3.14159
val gravity: Float = 9.81f
val result = pi * 2  // Double arithmetic

Boolean型

val isOnline: Boolean = true
val isEmpty = false
println(!isOnline)           // false
println(isOnline && !isEmpty) // true

Char型

val letter: Char = 'A'
val digit: Char = '7'
val emoji: Char = '\u2764'  // heart
println(letter.code)         // 65 (ASCII)

型推論の実例

val count = 10        // Int
val ratio = 0.75      // Double
val active = true     // Boolean
val initial = 'K'     // Char

読みやすさのための数値リテラルのアンダースコア

val million = 1_000_000
val hex = 0xFF_AA_BB
val binary = 0b1010_1010
println(million) // 1000000

数値の変換

val x: Int = 42
val y: Long = x.toLong()    // explicit
val z: Double = x.toDouble()
println("$y $z")

Stringはプリミティブ型ではない

val name: String = "Kotlin"
println(name.length)         // 6
println(name.uppercase())    // KOTLIN
println(name[0])             // K (Char)

Any、Nothing、Unit

fun greet(): Unit { println("Hi") }
fun fail(): Nothing { throw Exception("!!") }
val x: Any = 42  // Any accepts anything

isによる型の確認

val obj: Any = "Hello"
if (obj is String) {
    println(obj.length) // smart cast: no cast needed!
}

確認問題

まとめ