MainActivity.kt

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            DefaultTheme {
                CalendarApp()
            }
        }
    }
}

@Composable
fun CalendarApp(){

    // 시간에 대한 정보
    val calendarInstance = Calendar.getInstance()
    val time = remember {
        mutableStateOf(calendarInstance)
    }

    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(20.dp),
        horizontalAlignment = Alignment.CenterHorizontally
    ) {
        CalendarHeader(time)
    }

}

@Composable
fun CalendarHeader(date: MutableState<Calendar>) {

    // xxxx년 00월
    val resultTime = SimpleDateFormat("yyyy년 MM월", Locale.KOREA).format(date.value.time)

    Text(
        text = resultTime,
        fontSize = 30.sp
    )

}

@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
    DefaultTheme {
        CalendarApp()
    }
}