Java Collection sort

Question

I am trying to sort a list of Dates and it's not working.

Here is the declaration and get function in AttEnt

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "end_time")
private Date endTime;

public Date getEndTime() {
    return endTime;
}

Here is the sorting code that isn't doing anything. GetAttempts() gets the list of all the attempts for called. They aren't in order, and I just want to be able to get whatever attempt has the latest endTime.

            List<AttEnt> attempts = called.getAttempts();
            Collections.sort(attempts, new Comparator<AttEnt>() {
            @Override
            public int compare(AttEnt a1, AttEnt a2) {
                if (a1.getEndTime() == null || a2.getEndTime() == null)
                    return 0;
                return a1.getEndTime().compareTo(a2.getEndTime());
                }
            });

I believe that the code above should sort attempts, and then after it attempts should be sorted, so the latest end time would be attempts.get(attempts.size()-1).getEndTime()

What is the output you get, and what is the output you want? Consider creating a Minimal, Complete, and Verifiable example. — Robin Topper
– Robin Topper, Commented Apr 28, 2017 at 20:18
By the way - Comparator.comparing(AttEnt::getEndTime) is I believe better than writing a custom comparator. It compares the values based on the natural ordering of the type extracted using the passed method reference. — Adrian Jałoszewski
– Adrian Jałoszewski, Commented Apr 28, 2017 at 20:24

Trash Can · Accepted Answer · 2017-04-28 20:23:11Z

1

Comparator<AttEnt> comparator = Comparator.comparing(AttEnt::getEndTime).reversed();
attempts.sort(comparator);

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answered Apr 28, 2017 at 20:23

Trash Can

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5 Comments

Trash Can Over a year ago

Make sure your AttEnt.getEndTime does not return null

Trash Can Over a year ago

My bad Comparator<AttEnt> comparator = Comparator.reverseOrder().thenComparing(AttEnt::getEndTime)

Trash Can Over a year ago

How about this time Comparator<AttEnt> comparator = Comparator.reverseOrder().thenComparing(Comparator.comparing(AttEnt::getEndTime)) Sorry, I haven't used the other methods for along time, so quite forget their API docs. But this time it should work

ralyn Over a year ago

Still doesn't like that line.

ralyn Over a year ago

I tried this also, and it doesn't work either Collections.sort(attempts, (a1, a2) -> a1.getEndTime().compareTo(a2.getEndTime()));

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