Code:

Calendar cal = Calendar.getInstance();
      System.out.println("current date: " + cal.getTime());
      cal.add(Calendar.MINUTE, 7);
      SimpleDateFormat df = new SimpleDateFormat("HH:mm");
      System.out.println("7 minutes later: " + df.format(cal.getTime()));


cal.add(Calendar.MINUTE, 7);
.what to add to (can be days seconds...)
,7 : how many to add :ON: