Convert time slot to "00:00:00" format.

Convert time slot.java

String convertTime(long start_time, long end_time)
{
  String result = "00:00:00";
  
  if (end_time > start_time)
  {
    long time = end_time - start_time;
  
    long time_hour = TimeUnit.MILLISECONDS.toHours(time);
    time -= TimeUnit.HOURS.toMillis(time_hour);
    long time_min = TimeUnit.MILLISECONDS.toMinutes(time);
    time -= TimeUnit.MINUTES.toMillis(time_min);
    long time_seg = TimeUnit.MILLISECONDS.toSeconds(time);
    
    result = String.format("%02d:%02d:%02d", time_hour, time_min, time_seg);
  }
  
  return result;
}