Basic Kotlin Language
Variable 变量
var a: String = "initial" // Declares a mutable variable and initializing itval b: Int = 1 // Declares an immutable variable and initializing itval c = 3 var e: Int println(e) // 不可变量在使用前需要初始化 compiler error: it must be initialized before the first read. Function 函数
默认参数，命名参数 Default Parameter Values and Named Arguments
fun printMessage(message: String): Unit { // 1 println(message)}fun printMessageWithPrefix(message: String, prefix: String = "Info") { // 2 println("[$prefix] $message")}fun sum(x: Int, y: Int): Int { // 3 return x + y}fun multiply(x: Int, y: Int) = x * y Infix Functions 中缀函数
infix fun Int.times(str: String) = str.repeat(this) // 1 println(2 times "Bye ") // 2 val pair = "Ferrari" to "Katrina" // 3 println(pair) infix fun String.onto(other: String) = Pair(this, other) // 4 val myPair = "McLaren" onto "Lucas" println(myPair) class Person(val name: String) { val likedPeople = mutableListOf<Person>() infix fun likes(other: Person) { likedPeople.add(other) } // 6 } val sophia = Person("Sophia") val claudia = Person("Claudia") sophia likes claudia Operator Functions 操作符函数
operator fun Int.times(str: String) = str.repeat(this) // 1println(2 * "Bye ") // 2operator fun String.get(range: IntRange) = substring(range) // 3val str = "Always forgive your enemies; nothing annoys them so much."println(str[0..14]) vararg Parameters 可变参数函数
fun printAll(vararg messages: String) { // 1 for (m in messages) println(m)}printAll("Hello", "Hallo", "Salut", "Hola", "你好") // 2fun printAllWithPrefix(vararg messages: String, prefix: String) { // 3 for (m in messages) println(prefix + m)}printAllWithPrefix( "Hello", "Hallo", "Salut", "Hola", "你好", prefix = "Greeting: " // 4)fun log(vararg entries: String) { printAll(*entries) // 5}Control Flow 控制流
When
fun cases(obj: Any) { when (obj) { // 1 1 -> println("One") // 2 "Hello" -> println("Greeting") // 3 is Long -> println("Long") // 4 !is String -> println("Not a string") // 5 else -> println("Unknown") // 6 } }val result = when (obj) { // 1 1 -> "one" // 2 "Hello" -> 1 // 3 is Long -> false // 4 else -> 42 // 5 }循环
val cakes = listOf("carrot", "cheese", "chocolate")for (cake in cakes) { // 1 println("Yummy, it's a $cake cake!")} while (cakesEaten < 5) { // 1 eatACake() cakesEaten ++ } do { // 2 bakeACake() cakesBaked++ } while (cakesBaked < cakesEaten)Ranges
for(i in 0..3) { // 1 print(i)} for(i in 2..8 step 2) { // 2 print(i)}for (i in 3 downTo 0) { // 3 print(i)}以上都是双闭区间
Reference 参考
- kotlin Example