🟠 Kotlin 치트시트

var name = "Kotlin"
val age = 25
var isActive = true
val maxSize: Int = 1000

if (condition) {
    statement
} else if (otherCondition) {
    otherStatement
} else {
    defaultStatement
}

for (i in 0 until 10) {
    println(i)
}

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

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

fun greet(name: String) {
    println("Hello, $name!")
}

class Person(val name: String, var age: Int) {
    fun greet(): String {
        return "Hello, I'm $name"
    }
    
    fun haveBirthday() {
        age++
    }
}

data class User(
    val id: Int,
    val name: String,
    val email: String
)

val user = User(1, "Alice", "alice@example.com")
val (id, name, email) = user // 구조 분해

interface Drawable {
    fun draw()
}

class Circle(private val radius: Double) : Drawable {
    override fun draw() {
        println("Drawing a circle with radius $radius")
    }
}

fun String.isEmail(): Boolean {
    return this.contains("@") && this.contains(".")
}

val email = "user@example.com"
val isValid = email.isEmail()

var nullableName: String? = "John"
var nonNullName: String = "Jane"

nullableName = null // OK
// nonNullName = null // 컴파일 에러!

val length = nullableName?.length
val upperCase = nullableName?.uppercase()

val name = nullableName ?: "Unknown"
val length = nullableName?.length ?: 0

nullableName?.let { name ->
    println("Name is $name")
    println("Length is ${name.length}")
}