object

출처 https://www.youtube.com/watch?v=Q5noYbbc9uc [Code with Joyce]
object로 클래스를 정의하면, 싱클턴(Singleton) 패턴이 적용되어 객체가 한번만 생성

object Foo {
    fun bar(): String {
        return "foo.bar"
    }
}

fun main() {
    println(Foo.bar())
}

// 결과값 foo.bar

=================================================

// 출처 https://link2me.tistory.com/1787
object Singleton{
    init {
        println("Singleton class invoked.")
    }
    var variableName = "홍길동"
    fun printVarName(){
        println("변수명 : ${variableName} ")
    }
}

fun main() {
    Singleton.printVarName()

    println("\nSingleton variableName Change")
    Singleton.variableName = "강감찬"
    var a = A()
}

class A {
    init {
        println("Class init method. Singleton variableName property : ${Singleton.variableName}")
        Singleton.printVarName()
    }
}

//결과값
// Singleton class invoked.
// 변수명 : 홍길동 

// Singleton variableName Change
// Class init method. Singleton variableName property : 강감찬
// 변수명 : 강감찬