How to check if the list of intervals (Joda-Time) fully covers a month in Java

Question

I use the Joda-Time library in Java to track the list of time intervals . I want to check if the list of Interval objects is completely closed every minute of the month. There are about 30 intervals of different lengths from several hours to several days.

I thought that a cheap way to do this is to sort the list of intervals by start time, and then sequentially check if there is a gap between the intervals within the month range. If so, then the month is not fully covered.

I am stuck in the first part, sorting a list. I planned to use Arrays .sort (), but it needs elements to implement a comparable interface. However, looking at the source, the Joda-Time Interval class does not seem to have one that I can override, and I cannot extend it to write my own compareTo method.

Besides writing my own sorting method, does anyone know an easier way to do this? Thanks

Answer 1

You can use the following method

static boolean covers(Interval month, List<Interval> intervals) { //assumes intervals are sorted already on start times final MutableInterval monthInterval = new MutableInterval(month); start: for (final Interval interval : intervals) { if (interval.getStartMillis() <= monthInterval.getStartMillis() && interval.getEndMillis() > monthInterval.getStartMillis()) { if (interval.getEndMillis() > monthInterval.getEndMillis()) { return true; } monthInterval.setStartMillis(interval.getEndMillis()); // continue start; // loop continues regardless } else { if (interval.overlaps(month)) return false; } } return monthInterval.getStartMillis()== monthInterval.getEndMillis(); } 

Example

  static final List<Interval> intervals = new ArrayList<Interval>(); static { intervals.add(new Interval(new DateTime(1990, 05, 15, 00, 00, 00, 00), new DateTime(1990, 05, 18, 00, 00, 00, 00))); intervals.add(new Interval(new DateTime(1990, 04, 28, 00, 00, 00, 00), new DateTime(1990, 05, 18, 00, 00, 00, 00))); intervals.add(new Interval(new DateTime(1990, 05, 17, 00, 00, 00, 00), new DateTime(1990, 05, 21, 00, 00, 00, 00))); intervals.add(new Interval(new DateTime(1990, 05, 21, 00, 00, 00, 00), new DateTime(1990, 05, 29, 00, 00, 00, 00))); intervals.add(new Interval(new DateTime(1990, 05, 22, 00, 00, 00, 00), new DateTime(1990, 05, 25, 00, 00, 00, 00))); intervals.add(new Interval(new DateTime(1990, 05, 27, 00, 00, 00, 00), new DateTime(1990, 06, 02, 00, 00, 00, 00))); } public static void main(String[] args) { final DateTime startOfMonth = new DateTime(1990, 05, 01, 00, 00); final Interval monthInterval = new Interval(startOfMonth, startOfMonth.plusMonths(1)); covers(monthInterval, intervals); } static boolean covers(Interval month, List<Interval> intervals) { final MutableInterval monthInterval = new MutableInterval(month); start: for (final Interval interval : intervals) { if (interval.getStartMillis() <= monthInterval.getStartMillis() && interval.getEndMillis() > monthInterval.getStartMillis()) { if (interval.getEndMillis() > monthInterval.getStartMillis()) { return true; } monthInterval.setStartMillis(interval.getEndMillis()); continue start; } } return monthInterval.getStartMillis()== monthInterval.getEndMillis(); } 

Answer 2

Use Comparator to sort time intervals and use Interval#gap to check spaces. The following code returns true if the interval between the beginning and the end is completely covered by timeIntervals:

 public static boolean isCovered(List<Interval> timeIntervals, DateTime start, DateTime end) { if (timeIntervals.isEmpty()) { return false; } // create sorted set from original List to get // sorted intervals without double entries Set<Interval> intervalSet = new TreeSet<>(new Comparator<Interval>() { @Override public int compare(Interval o1, Interval o2) { return o1.getStart().compareTo(o2.getStart()); } }); intervalSet.addAll(timeIntervals); List<Interval> intervals = new ArrayList<>(intervalSet); // remove intervals completely contained in others List<Interval> removedIntervals = new ArrayList<>(); for (int i = 0; i < (intervals.size()-1); i++) { for (int j = (i+1); j < intervals.size(); j++) { if (intervals.get(i).contains(intervals.get(j))) { if (!removedIntervals.contains(intervals.get(j))) { removedIntervals.add(intervals.get(j)); } } } } intervals.removeAll(removedIntervals); if (intervals.get(0).getStart().isAfter(start) || intervals.get(intervals.size() - 1).getEnd().isBefore(end)) { return false; } // check for gaps for (int i = 0; i < (intervals.size() - 1); i++) { Interval gap = intervals.get(i).gap(intervals.get(i+1)); if (gap != null && new Interval(start, end).overlaps(gap)) { // gap detected between interval i and interval (i+1) return false; } } return true; }