DateTime.md

1. Calendar

1.1. Convert Milliseconds to Converted String by Datetime format, Use DataFormat Function

var calendar:Calendar = Calendar.getInstance(Locale.KOREA);
var date:Long = calendar.timeInMillis // Milliseconds of Now Date, Use Instead of getTimeInMillis
var result:String = DataFormat.format("YYmmdd" Date(date)).toString();

1.2. Convert Milliseconds to Converted String by Datetime Pattern, Use SimpleDateFormat Function

var calendar:Calendar = Calendar.getInstance(Locale.KOREA);
var date:Long = calendar.timeInMillis // Milliseconds of Now Date, Use Instead of getTimeInMillis
val pattern = "MM-dd-yyyy"
val simpleDateFormat = SimpleDateFormat(pattern)
val date = simpleDateFormat.format(Date(now))

1.3. Convert Formatted String to Formatted String, Use SimpleDateFormat Function

var calendar:Calendar = Calendar.getInstance(Locale.KOREA);
var date:Long = calendar.timeInMillis // Milliseconds of Now Date, Use Instead of getTimeInMillis
val pattern = "MM-dd-yyyy"
val simpleDateFormat = SimpleDateFormat(pattern)
val date = simpleDateFormat.parse("12-01-2018")

2. TimeUnit

2.1. Convert millisecodns to Hours/Minutes/Seconds

var milliseconds = 1000L
TimeUnit.MILLISECONDS.toHours(milliseconds)
TimeUnit.MILLISECONDS.toMinutes(milliseconds)
TimeUnit.MILLISECONDS.toSeconds(milliseconds)

3. SimpleDateFormat

3.1. String to Milliseconds

var dateFormat: SimpleDateFormat = SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); // Use Want DateTime Format

try {
    var mDate: Date = dateFormat.parse(date);
    var timeInMilliseconds:Long = mDate.getTime();
} catch (e: ParseException) {
    print(e.printStackTrace())
}

3.2. Parse String

var date:Date = SimpleDateFormat("yyyy.MM.dd").parse("2019.05.23".toString())

3.3. Convert to Other Format

var date:Date = SimpleDateFormat("yyyy.MM.dd").parse("2019.05.23".toString())
var dateStr:String = SimpleDateFormat("yyyy-MM-dd").format(date)

4. GregorianCalendar

4.1. Get Format of One Month Ago Date

val c = GregorianCalendar()
val sdf = SimpleDateFormat("yyyy.MM.dd")
c.setTime(Date())
var currentTime = sdf.format(c.time)
c.add(Calendar.WEEK_OF_MONTH, -1);
var oneMonthAgoTime = sdf.format(c.time)