How to round time to the nearest quarter hour in java?

Question

Given today\'s time e.g. 2:24PM, how do I get it to round to 2:30PM?

Similarly if the time was 2:17PM, how do I get it to round to 2:15PM?

Answer 1

if you have the minutes you can round them with the following function:
int minutes = i % 15 < 8 ? i / 15 * 15 : (i / 15 + 1) * 15;

Answer 2

Use the following functions to get the minutes rounded to last quarter getRecentQuater():Date, getSysDate_LastQuarterMins("dd.MM.yyyy HH:mm:ss"):String: ^{Converting LocalDateTime to Date}

public static Date getRecentQuater() {
    LocalDateTime time = LocalDateTime.now();
    LocalDateTime lastQuarter = time.truncatedTo(ChronoUnit.HOURS).plusMinutes(getLastQuarterValue(time.getMinute()));
    System.out.println("lastQuarter LocalDateTime: " + lastQuarter);

    Date date = Date.from(lastQuarter.atZone(ZoneId.systemDefault()).toInstant());
    System.out.println("lastQuarter Date: " + lastQuarter);
    return date;
}
public static String getSysDate_LastQuarterMins(String dateFormat) {
    Date date = getRecentQuater();
    SimpleDateFormat ft = new SimpleDateFormat (dateFormat);
    String sysDate_RoundMin = ft.format(date);
    System.out.println("getSysDate_LastQuarterMins() LocalDateTime : "+sysDate_RoundMin);
    return sysDate_RoundMin;
}

getSysDate_LastQuarterMins() : Mon Jan 20 17:30:00 CET 2020

public static Date getSysDate_LastQuarterMins() {
    Calendar cal = Calendar.getInstance();
    cal.setTime( new Date(System.currentTimeMillis()) );

    int min = cal.get(Calendar.MINUTE);

    cal.set(Calendar.MINUTE, getLastQuarterValue(min));
    cal.set(Calendar.SECOND, 00);
    Date lastQuarter = cal.getTime();
    System.out.println("getSysDate_LastQuarterMins() Calendar : "+lastQuarter);
    return lastQuarter;
}

You can find the LastQuarter Value Round value from the follwing fucntions, provided with some outputs on function call diaplayLastQuarter_RoundValue(min):

Min: 10, LastQuarter:  0, Round: 15
Min: 24, LastQuarter: 15, Round: 30
Min: 36, LastQuarter: 30, Round: 30
Min: 37, LastQuarter: 30, Round: 30
Min: 38, LastQuarter: 30, Round: 45
Min: 39, LastQuarter: 30, Round: 45
Min: 44, LastQuarter: 30, Round: 45
Min: 57, LastQuarter: 45, Round: 00 [57, 07:45:00, 08:00:00]

public static void diaplayLastQuarter_RoundValue(int minutes) {
    System.out.format("Min: %2d, LastQuarter: %2d, Round: %2d\n",
            minutes, getLastQuarterValue(minutes), getRoundValue(minutes));
}
public static int getLastQuarterValue(int minutes) {
    int min = 15 * (minutes / 15);
    //System.out.println("Min: "+minutes+", getLastQuarterValue : "+ min);
    return min;
}
public static int getRoundValue(int minutes) {
    getLastQuarterValue(minutes);
    int minRound = (int) (Math.round(minutes / 15.0) * 15.0);
    //System.out.println("Min: "+minutes+", getRoundValue : "+minRound);
    return minRound;
}