익명 객체와 객체 식

객체 표현식

익명으로 인터페이스 구현하기

interface ClickListener {
    fun onClick(): String
}
fun main() {
    val listener = object : ClickListener {
        override fun onClick() = "clicked!"
    }
    println(listener.onClick())
}

상태를 가진 익명 클래스

fun main() {
    val counter = object {
        var count = 0
        fun inc() { count++ }
        fun show() = println("count = $count")
    }
    counter.inc(); counter.inc(); counter.inc()
    counter.show()
}

익명 객체의 타입

fun main() {
    val pair = object {
        val left = "L"
        val right = "R"
    }
    println("${pair.left} and ${pair.right}")
}

익명 타입 노출

fun makeListener() = object {
    fun greet() = "hello"
}
fun main() {
    val l = makeListener()
    println(l.greet()) // OK — same compilation unit
}

여러 인터페이스

interface Closeable { fun close() }
interface Flushable { fun flush() }
fun main() {
    val resource = object : Closeable, Flushable {
        override fun close() = println("closed")
        override fun flush() = println("flushed")
    }
    resource.flush()
    resource.close()
}

클래스 확장하기

open class Animal(val name: String) {
    open fun speak() = "$name makes a sound"
}
fun main() {
    val pet = object : Animal("Rex") {
        override fun speak() = "$name barks!"
    }
    println(pet.speak())
}

둘러싼 변수 캡처

fun main() {
    var log = mutableListOf<String>()
    val recorder = object {
        fun record(s: String) { log.add(s) }
    }
    recorder.record("event 1")
    recorder.record("event 2")
    println(log)
}

익명 객체를 사용할 때

fun main() {
    val nums = listOf(3, 1, 4, 1, 5, 9, 2, 6)
    val sorted = nums.sortedWith(object : Comparator<Int> {
        override fun compare(a: Int, b: Int) = b - a // descending
    })
    println(sorted)
}

가능하면 람다 우선

fun main() {
    val nums = listOf(3, 1, 4, 1, 5, 9)
    // Old way:
    val sorted1 = nums.sortedWith(object : Comparator<Int> {
        override fun compare(a: Int, b: Int) = b - a
    })
    // New way — SAM conversion:
    val sorted2 = nums.sortedWith(Comparator { a, b -> b - a })
    println("$sorted1 / $sorted2")
}

익명 객체와 선언된 객체

// Named singleton (one instance, accessed globally)
object GlobalLogger { fun log(m: String) = println("[L] $m") }
// Anonymous (created at expression evaluation)
fun main() {
    val local = object { fun hi() = "hi" }
    GlobalLogger.log("hello")
    println(local.hi())
}

빠른 확인

요약