Kotlin - Sizuha/devdog GitHub Wiki

// Kotlin
var s: String = "abc"
val t: String = "xyz"

var s = "abc"
val t = "xyz"

val oneMillion = 1_000_000
val creditCardNumber = 1234_5678_9012_3456L
val socialSecurityNumber = 999_99_9999L
val hexBytes = 0xFF_EC_DE_5E
val bytes = 0b11010010_01101001_10010100_10010010

Char

var b: Boolean = true
b = false

// Creates an Array<String> with values ["0", "1", "4", "9", "16"]
val asc = Array(5, { i -> (i * i).toString() })

val x: IntArray = intArrayOf(1, 2, 3)
x[0] = x[1] + x[2]

val s: String = "Hello, world!\n"

val text = """
    |Tell me and I forget.
    |Teach me and I remember.
    |Involve me and I learn.
    |(Benjamin Franklin)
    """.trimMargin()

fun main(args: Array<String>) {
    println("---")
    println("""
    |for (i = 0; i < 100; ++i)
      |console.log(i)
    """.trimMargin())
    println("---")
    println("""
    > a
    > b
    > c
    > d
    """.trimMargin("> "))
    println("---")
}

fun main(args: Array<String>) {
    println("---")
    println("""
    for (i = 0; i < 100; ++i)
      console.log(i)
    """.trimIndent())
    println("---")
}

val i = 10
val s = "i = $i" // evaluates to "i = 10"

val s = "abc"
val str = "$s.length is ${s.length}" // evaluates to "abc.length is 3"

val price = """
${'$'}9.99
"""

import foo.Bar // Bar is now accessible without qualification
import foo.* // everything in 'foo' becomes accessible
import bar.Bar as bBar // bBar stands for 'bar.Bar'

// Traditional usage 
var max = a 
if (a < b) max = b

// With else 
var max: Int
if (a > b) {
    max = a
} 
else {
    max = b
}
 
// As expression 
val max = if (a > b) a else b

val max = if (a > b) {
    print("Choose a")
    a
} else {
    print("Choose b")
    b
}

when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> { // Note the block
        print("x is neither 1 nor 2")
    }
}

when (x) {
    0, 1 -> print("x == 0 or x == 1")
    else -> print("otherwise")
}

when (x) {
    parseInt(s) -> print("s encodes x")
    else -> print("s does not encode x")
}

when (x) {
    in 1..10 -> print("x is in the range")
    in validNumbers -> print("x is valid")
    !in 10..20 -> print("x is outside the range")
    else -> print("none of the above")
}

// As expression (1)
fun hasPrefix(x: Any) = when(x) {
    is String -> x.startsWith("prefix")
    else -> false
}

// As expression (2) 
val groupCode  = when(number) {
    0 -> 0
    in 1..10 -> 1
    in 11..100 -> 2
    else -> 3
}

when {
    x.isOdd() -> print("x is odd")
    x.isEven() -> print("x is even")
    else -> print("x is funny")
}

for (item: Type in Collection) {
    // ...
}

for ((index, value) in array.withIndex()) {
    println("the element at $index is $value")
}

// 기본적으로 range 표현을 이용한다.

// 1.
for (i in 1..100) { ... }

// 2.
(1..100).forEach { i -> }

while (x > 0) {
    x--
}

do {
    val y = retrieveData()
} while (y != null) // y is visible here!

loop@ for (i in 1..100) {
    for (j in 1..100) {
        if (...) break@loop
    }
}

fun foo() {
    ints.forEach lit@ {
        if (it == 0) return@lit
        print(it)
    }
}

fun foo() {
    ints.forEach {
        if (it == 0) return@forEach
        print(it)
    }
}

for (i in 1..100) {
    print(i)
}

for (i in 1 until 100) {
    print(i)
}

for (i in 0..100 step 2) {
    print(i)
}

for (i in 100 downTo 0 step 2) {
    print(i)
}

class Some {

}

class Person constructor(firstName: String) {
}
//--- or ---//
class Person(firstName: String) {
}

class AClass(some: String) {	
	lateinit var field: String

	init {
		field = some
	}
}
//--- or ---//
class AClass(some: String) {	
	val field: String = some
}
//--- or ---//
class AClass(val field: String) {	
}

class Person {
    constructor(parent: Person) {
        parent.children.add(this)
    }
}

class Person(val name: String) {
    constructor(name: String, parent: Person) : this(name) {
        parent.children.add(this)
    }
}

class Constructors {
    init {
        println("Init block")
    }

    constructor(i: Int) {
        println("Constructor")
    }
}

class Customer(val customerName: String = "") {}

val customer = Customer("Joe Smith")

class AClass {
    var name: String
        get() = this.toString()
        set(value) { name = value }
}

class AClass {
    var name: String
        get() = this.toString()
        private set
}

class Outer {
    private val bar: Int = 1
    class Nested {
        fun foo() = 2
    }
}

val demo = Outer.Nested().foo() // == 2

class Outer {
    private val bar: Int = 1
    inner class Inner {
        fun foo() = bar
    }
}

val demo = Outer().Inner().foo() // == 1

window.addMouseListener(object: MouseAdapter() {
    override fun mouseClicked(e: MouseEvent) {
        // ...
    }
                                                                                                            
    override fun mouseEntered(e: MouseEvent) {
        // ...
    }
})

open class Base {
    open fun v() {}
    fun nv() {}
}
class Derived() : Base() {
    override fun v() {}
}

// 정의
interface ISome {
	var fieldA: String // 프로퍼티
	val fieldB: String // 프로퍼티

	fun testA()
	fun testB(): Boolean { return true } // 기본 동작을 지정할 수 있다
}

// 사용
class SomeClass : ISome {
	override var fieldA
		get() = "TEST"
		private set

	override val fieldB = "TEST2"
	override fun testA { /* ... */ }
}

fun <T> someFunc() { ... }

// T에 대한 타입 조건을 추가
fun <T: SomeType> someFunc() { ... }

// T에 대한 여러개의 타입 조건을 추가
fun <T> someFunc() 
where T: SomeTypeA, T: SomeTypeB
{ ... }

// 물론 제네릭 타입을 여러개 지정할 수도 있다
fun <E, R> someFunc() { ... }

class SomeClass<T> {
// . . .
}

class SomeClass<T: SomeType> {
// . . .
}

class SomeClass<T> 
where T: SomeTypeA, T: SomeTypeB {
// . . .
}

interface ISome<out T> {
	fun someFunc(): T
}

interface ISome<in T> {
	fun someFunc(a: T)
}

@Target(AnnotationTarget.FIELD, AnnotationTarget.PROPERTY)
annotation class Column(
        val name: String,
        val notNull: Boolean = false,
        val unique: Boolean = false,
        val exclude: Boolean = false
)

for (member in some::class.memberProperties) {
	// 어노테이션 탐색(1)
	member.annotations.forEach { a: Annotation -> 
		// ...
	}

	// 어노테이션 탐색(2)
	member.findAnnotation<AnnotationType>()?.let { /* ... */ }
}

for (member in some::class.memberProperties) {
	when (member.returnType) {
		Int::class.createType() -> { /* ... */ }
		else -> { /* ... */ }
	}
}

// member: KMutableProperty<*>

// 읽기
val r = member.getter.call(...)

// 쓰기
member.setter.call(...)

val accessible = member.isAccessible
member.isAccessible = true
member.setter.call(tableObj, value)
member.isAccessible = accessible

class NameCard {
    var name = ""
    var tel = ""
    var email = ""
}

val newCard: NameCard = NameCard().apply { // this = NameCard()
    name = "xxxxxx"
    tel = "000-0000-0000"
    email = "[email protected]"
    // 자동으로 this를 넘겨줌
}

val newCard: NameCard = NameCard().also { // it = NameCard()
    it.name = "xxxxxx"
    it.tel = "000-0000-0000"
    it.email = "[email protected]"
    // 자동으로 it을 넘겨줌
}

val newCard: NameCard()
newCard.run { // this = newCard
    name = "xxxxxx"
    tel = "000-0000-0000"
    email = "[email protected]"
}

val newCard: NameCard()
newCard.let { // it = newCard
    it.name = "xxxxxx"
    it.tel = "000-0000-0000"
    it.email = "[email protected]"
}