How to use

add

method

in

java.util.Calendar

/**
 * Currently the instance config is expired by 1 day, add one more hour to avoid possible time
 * difference
 */
private Date getValidInstanceConfigDate() {
 Calendar cal = Calendar.getInstance();
 cal.add(Calendar.DATE, -1);
 cal.add(Calendar.HOUR, -1);
 return cal.getTime();
}

 String dt = "2008-01-01";  // Start date
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = Calendar.getInstance();
c.setTime(sdf.parse(dt));
c.add(Calendar.DATE, 1);  // number of days to add
dt = sdf.format(c.getTime());  // dt is now the new date

 // today    
Calendar date = new GregorianCalendar();
// reset hour, minutes, seconds and millis
date.set(Calendar.HOUR_OF_DAY, 0);
date.set(Calendar.MINUTE, 0);
date.set(Calendar.SECOND, 0);
date.set(Calendar.MILLISECOND, 0);

// next day
date.add(Calendar.DAY_OF_MONTH, 1);

@Test
public void testIncrementDayOfMonthByOne() throws Exception {
  CronTrigger trigger = new CronTrigger("* * * 10 * *", timeZone);
  calendar.set(Calendar.DAY_OF_MONTH, 9);
  Date date = calendar.getTime();
  calendar.add(Calendar.DAY_OF_MONTH, 1);
  calendar.set(Calendar.HOUR_OF_DAY, 0);
  calendar.set(Calendar.MINUTE, 0);
  calendar.set(Calendar.SECOND, 0);
  TriggerContext context = getTriggerContext(date);
  assertEquals(calendar.getTime(), trigger.nextExecutionTime(context));
}

public static List<String> getOldWeekDays() {
  final Calendar c = Calendar.getInstance();
  String[] months = new String[8];
  for (int i = 0; i < 8; i++) {
    months[i] = new SimpleDateFormat("MM.dd").format(new Date(c
        .getTimeInMillis()));
    c.add(Calendar.DAY_OF_MONTH, -1);
  }
  return Arrays.asList(months);
}

calendar.setTime(date);
calendar.set(Calendar.MILLISECOND, 0);
long originalTimestamp = calendar.getTimeInMillis();
doNext(calendar, calendar.get(Calendar.YEAR));
if (calendar.getTimeInMillis() == originalTimestamp) {
  calendar.add(Calendar.SECOND, 1);
  doNext(calendar, calendar.get(Calendar.YEAR));
return calendar.getTime();

public static String getCurrentDay2() {
  String curDateTime = null;
  try {
    SimpleDateFormat mSimpleDateFormat = new SimpleDateFormat(dateFormatYMDHMS);
    Calendar c = new GregorianCalendar();
    c.add(Calendar.DAY_OF_MONTH, 0);
    curDateTime = mSimpleDateFormat.format(c.getTime());
  } catch (Exception e) {
    e.printStackTrace();
  }
  return curDateTime;
}

 Date whateverDateYouWant = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(whateverDateYouWant);

int unroundedMinutes = calendar.get(Calendar.MINUTE);
int mod = unroundedMinutes % 15;
calendar.add(Calendar.MINUTE, mod < 8 ? -mod : (15-mod));

private Timestamp getTomorrow() {
  Calendar c = Calendar.getInstance();
  c.setTime(getToday());
  c.add(Calendar.DATE, 1);
  return new Timestamp(c.getTimeInMillis());
}

private SimpleDateFormat(Locale locale) {
  numberFormat = NumberFormat.getInstance(locale);
  numberFormat.setParseIntegerOnly(true);
  numberFormat.setGroupingUsed(false);
  calendar = new GregorianCalendar(locale);
  calendar.add(Calendar.YEAR, -80);
  creationYear = calendar.get(Calendar.YEAR);
  defaultCenturyStart = calendar.getTime();
}

protected Date calculateDueDate(CommandContext commandContext, int waitTimeInSeconds, Date oldDate) {
 Calendar newDateCal = new GregorianCalendar();
 if (oldDate != null) {
  newDateCal.setTime(oldDate);
 } else {
  newDateCal.setTime(commandContext.getProcessEngineConfiguration().getClock().getCurrentTime());
 }
 newDateCal.add(Calendar.SECOND, waitTimeInSeconds);
 return newDateCal.getTime();
}

protected Calendar nextDay(Date date, int dayOfWeek) {
 calendar.setTime(date);
 int currDayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
 int daysToAdd;
 if (currDayOfWeek < dayOfWeek) {
  daysToAdd = dayOfWeek - currDayOfWeek;
 } else {
  daysToAdd = 7 - currDayOfWeek + dayOfWeek;
 }
 calendar.add(Calendar.DATE, daysToAdd);
 return calendar;
}

private static long gotoFirstDayOfWeek(Calendar cal){
  int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK);
  int firstDayOfWeek = cal.getFirstDayOfWeek();
  int shift = dayOfWeek >= firstDayOfWeek ? (dayOfWeek - firstDayOfWeek) : (dayOfWeek + 7 - firstDayOfWeek);
  cal.add(Calendar.DAY_OF_MONTH, -shift);
  return cal.getTimeInMillis();
}

protected static long doUpdateCurrentMonth(Calendar working, CronEntry month) throws MessageFormatException {
  int currentMonth = working.get(Calendar.MONTH) + 1;
  if (!isCurrent(month, currentMonth)) {
    int nextMonth = getNext(month, currentMonth, working);
    working.add(Calendar.MONTH, nextMonth);
    // Reset to start of month.
    resetToStartOfDay(working, 1);
    return working.getTimeInMillis();
  }
  return 0L;
}

private int findNextDay(Calendar calendar, BitSet daysOfMonth, int dayOfMonth, BitSet daysOfWeek, int dayOfWeek,
    List<Integer> resets) {
  int count = 0;
  int max = 366;
  // the DAY_OF_WEEK values in java.util.Calendar start with 1 (Sunday),
  // but in the cron pattern, they start with 0, so we subtract 1 here
  while ((!daysOfMonth.get(dayOfMonth) || !daysOfWeek.get(dayOfWeek - 1)) && count++ < max) {
    calendar.add(Calendar.DAY_OF_MONTH, 1);
    dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
    dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
    reset(calendar, resets);
  }
  if (count >= max) {
    throw new IllegalArgumentException("Overflow in day for expression \"" + this.expression + "\"");
  }
  return dayOfMonth;
}

 Calendar c = Calendar.getInstance(); 
c.setTime(dt); 
c.add(Calendar.DATE, 1);
dt = c.getTime();

@Test
public void testIncrementDayOfMonthAndRollover() throws Exception {
  CronTrigger trigger = new CronTrigger("* * * 10 * *", timeZone);
  calendar.set(Calendar.DAY_OF_MONTH, 11);
  Date date = calendar.getTime();
  calendar.add(Calendar.MONTH, 1);
  calendar.set(Calendar.DAY_OF_MONTH, 10);
  calendar.set(Calendar.HOUR_OF_DAY, 0);
  calendar.set(Calendar.MINUTE, 0);
  calendar.set(Calendar.SECOND, 0);
  TriggerContext context = getTriggerContext(date);
  assertEquals(calendar.getTime(), trigger.nextExecutionTime(context));
}

/**
 * Sets the Date and Cache headers for the HTTP Response
 *
 * @param response    HTTP response
 * @param fileToCache file to extract content type
 */
private static void setDateAndCacheHeaders(HttpResponse response, File fileToCache) {
 SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
 dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));
 // Date header
 Calendar time = new GregorianCalendar();
 response.headers().set(DATE, dateFormatter.format(time.getTime()));
 // Add cache headers
 time.add(Calendar.SECOND, HTTP_CACHE_SECONDS);
 response.headers().set(EXPIRES, dateFormatter.format(time.getTime()));
 response.headers().set(CACHE_CONTROL, "private, max-age=" + HTTP_CACHE_SECONDS);
 response.headers().set(
     LAST_MODIFIED, dateFormatter.format(new Date(fileToCache.lastModified())));
}

 Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, -1);
System.out.println("Yesterday's date = "+ cal.getTime());

private int findNextDay(Calendar calendar, BitSet daysOfMonth, int dayOfMonth, BitSet daysOfWeek, int dayOfWeek,
    List<Integer> resets) {
  int count = 0;
  int max = 366;
  // the DAY_OF_WEEK values in java.util.Calendar start with 1 (Sunday),
  // but in the cron pattern, they start with 0, so we subtract 1 here
  while ((!daysOfMonth.get(dayOfMonth) || !daysOfWeek.get(dayOfWeek - 1)) && count++ < max) {
    calendar.add(Calendar.DAY_OF_MONTH, 1);
    dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
    dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
    reset(calendar, resets);
  }
  if (count >= max) {
    throw new IllegalArgumentException("Overflow in day for expression \"" + this.expression + "\"");
  }
  return dayOfMonth;
}