Something like this should do the trick:
Calendar cal = Calendar.getInstance();
cal.set(datepick.getYear(), datepick.getMonth() + 1, datepick.getDayOfMonth());
cal.add(Calendar.DATE, 120);
datepick.updateDate(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH) - 1, cal.get(Calendar.DATE));
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