比较两个 ZonedDateTime 并忽略 Zone

Question

Compare two ZonedDateTime with ignoring the Zone:

Example:

2022-08-17 03:30:00+02 compare 2022-08-17 03:30:00+01 must give true

I Have a stream that must compare each object with others using this Date:

Set<Tele> jPointsSet = jPoints.stream()
                .collect(Collectors.toCollection(() -> 
                                new TreeSet<>(Comparator.comparing(Tele::getDateM))));

the getDateM is ZonedDateTime so I would like when use Comparator.comparing(Tele::getDateM)) ignore the Zone

Answer 1

As @OH GOD SPIDERS said in the comments, you can extract LocalDateTime from a ZonedDateTime .

Comparator.comparing(tele -> tele.getDateM().toLocalDateTime())

But be aware that if two LocalDateTime instances are equal, it doesn't necessarily mean that they're describing the same point in time. In order to establish comparison based on a specific point in the global timeline, you need to use Instant .

Comparator.comparing(tele -> tele.getDateM().toInstant())

Sidenote: while dealing with a TreeSet , it's more handy to use NavigableSet interface as an abstract type. It gives you access to methods like pollFirst() , pollLast() , lower() , higher() , etc. which are not declared in the Set interface.