코틀린 kotlin에서 HashMap 사용하기/ key값만 출력하기/ HashMap 만들기 / 가변형 HashMap 만들기 예시

fun main(args: Array<String>) {

    //Map -> (key, value) -pair
    //< String, Object >

    val langMap: Map<Int,String> = mapOf( 1001 to "kotlin",1002 to "Java", 1003 to "react")
    for ((key, value) in langMap){
        println("key=$key, value=$value")
     }
    /*
    출력값
    key=1001, value=kotlin
    key=1002, value=Java
    key=1003, value=react
    */

    println(langMap[1002]) //출력값: Java
    println(langMap.get(1001)) //출력값: kotlin
    println(langMap) //출력값: {1001=kotlin, 1002=Java, 1003=react}
    println(langMap.keys) //출력값:[1001, 1002, 1003]

    //가변형 map
    val capitalCityMap:MutableMap<String, String> =
        mutableMapOf("japan" to "tokyo", "USA" to "washington", "German" to "Berlin")
    println(capitalCityMap)
    //출력값:{japan=tokyo, USA=washington, German=Berlin}
    println(capitalCityMap.keys)
    //출력값:[japan, USA, German]
    println(capitalCityMap.values)
    //출력값:[tokyo, washington, Berlin]

    capitalCityMap.put("UK","London") //추가
    capitalCityMap.remove("German") // 삭제
    println(capitalCityMap)
    //출력값: {japan=tokyo, USA=washington, UK=London}

    val addData = mutableMapOf("Denmark" to "Copenhagen","India" to "New Delhi")
    capitalCityMap.putAll(addData) //addDate 부분까지 통합
    println(capitalCityMap)
    //통합 후 출력값: {japan=tokyo, USA=washington, UK=London, Denmark=Copenhagen, India=New Delhi}
    

    //정렬
    //var sortedByValue = capitalCityMap.toList().sortedBy { it.first } //오름차순
    var sortedByValue = capitalCityMap.toList().sortedByDescending { it.first } //내림차순
    println(sortedByValue)
    //내림차순 출력값 
    //[(japan, tokyo), (USA, washington), (UK, London), (India, New Delhi), (Denmark, Copenhagen)]




}