Portfolio


package my.demo

import kotlin.text.*

// ...


fun main(args: Array<String>) {
    println(args.contentToString())
}


fun sum(a: Int, b: Int): Int {
    return a + b
}

fun sum(a: Int, b: Int) = a + b

fun printSum(a: Int, b: Int): Unit {
    println("sum of $a and $b is ${a + b}")
}

fun printSum(a: Int, b: Int) {
    println("sum of $a and $b is ${a + b}")
}


val a: Int = 1  // 즉시 할당
val b = 2   // `Int` 타입 추론
val c: Int  // 즉시 할당을 하지 않으면 타입을 제공 해야함
c = 3       // 연기된 할당


val b //This variable must either have a type annotation or be initialized

val c = 3;
c = 2 // Val cannot be reassigned


var x = 5 // `Int` type is inferred
x += 1


val PI = 3.14
var x = 0

fun incrementX() { 
    x += 1 
}


class Shape // 클래스 정의 - `class` 키워드

//클래스의 프로퍼티는 선언부 (declaration) 혹은 body 에 나열될 수 있음
class Rectangle(var height: Double, var length: Double) {
    var perimeter = (height + length) * 2;
}


val rectangle = Rectangle(5.0, 2.0)
println("The perimeter is ${rectangle.perimeter}")


open class Shape // 클래스 정의 - `class` 키워드

class Rectangle(var height: Double, var length: Double) : Shape() {
    var perimeter = (height + length) * 2;
}


var a = 1
// simple name in template:
val s1 = "a is $a" 

a = 2
// arbitrary expression in template:
val s2 = "${s1.replace("is", "was")}, but now is $a"


fun maxOf(a: Int, b: Int): Int {
    if (a > b) {
        return a
    } else {
        return b
    }
}


fun maxOf(a: Int, b: Int) = if (a > b) a else b


val items = listOf("apple", "banana", "kiwifruit")
for (item in items) {
    println(item)
}


val items = listOf("apple", "banana", "kiwifruit")
for (index in items.indices) {
    println("item at $index is ${items[index]}")
}


val items = listOf("apple", "banana", "kiwifruit")
var index = 0
while (index < items.size) {
    println("item at $index is ${items[index]}")
    index++
}


fun describe(obj: Any): String =
    when (obj) {
        1          -> "One"
        "Hello"    -> "Greeting"
        is Long    -> "Long"
        !is String -> "Not a string"
        else       -> "Unknown"
    }


val x = 10
val y = 9
if (x in 1..y+1) {
    println("fits in range")
}


val list = listOf("a", "b", "c")

if (-1 !in 0..list.lastIndex) {
    println("-1 is out of range")
}
if (list.size !in list.indices) {
    println("list size is out of valid list indices range, too")
}


for (x in 1..5) {
    print(x)
}
//12345


for (x in 1..10 step 2) {
    print(x)
}
//13579

println()
for (x in 9 downTo 0 step 3) {
    print(x)
}
//9630


fun main() {
    val items = listOf("apple", "banana", "kiwifruit")

    for (item in items) {
        println(item)
    }

}


fun main() {
    val items = setOf("apple", "banana", "kiwifruit")

    when {
        "orange" in items -> println("juicy")
        "apple" in items -> println("apple is fine too")
    }

}


fun main() {

    val fruits = listOf("banana", "avocado", "apple", "kiwifruit")
    fruits
      .filter { it.startsWith("a") }
      .sortedBy { it }
      .map { it.uppercase() }
      .forEach { println(it) }

}


//문자열이 정수값이 아니라면 null을 반환하는 paseInt 함수
fun parseInt(str: String): Int? {
    // ...
}


fun printProduct(arg1: String, arg2: String) {
    val x = parseInt(arg1)
    val y = parseInt(arg2)

    // Using `x * y` yields error because they may hold nulls.
    if (x != null && y != null) {
        // x and y are automatically cast to non-nullable after null check
        println(x * y)
    }
    else {
        println("'$arg1' or '$arg2' is not a number")
    }    
}


fun getStringLength(obj: Any): Int? {
    if (obj is String) {
        // `obj` is automatically cast to `String` in this branch
        return obj.length
    }

    // `obj` is still of type `Any` outside of the type-checked branch
    return null
}


fun getStringLength(obj: Any): Int? {
    // `obj` is automatically cast to `String` on the right-hand side of `&&`
    if (obj is String && obj.length > 0) {
        return obj.length
    }

    return null
}