Sorting of Date ArrayList

This is one of the Simplest way to sort,

Collections.sort(<Your Array List>);

If you have any special requirements while sorting, so you may do it by providing your own Comparator. For example:

//your List
ArrayList<Date> d = new ArrayList<Date>();

//Sorting
Collections.sort(d, new Comparator<Date>() {
    @Override
    public int compare(Date lhs, Date rhs) {
        if (lhs.getTime() < rhs.getTime())
            return -1;
        else if (lhs.getTime() == rhs.getTime())
            return 0;
        else
            return 1;
    }
});

The key element is that you are converting your Date object into milliseconds (using getTime()) for comparison.

After 8 years..

List<Date> dates = datelist;
List<Date> sorted = dates.stream()
  .sorted(Comparator.comparingLong(Date::getTime))
  .collect(Collectors.toList());

After 12 years...

final var sortedDates = dates.stream().sorted().toList();