Get the largest attribute value in a Collection of Objects in Java

Question

I have an object Patch that contains an Id, so let's say it has:

public class Patch {
    private Long id;

    public Patch(Long id) {
        this.id = id;
    }

    public Long getId() {
        return id;
    }
}

Let's say I have a Collection of those patches of size > 0. So the Collection can contain 1 Patch object, or 10 Patch objects. I want to get the id value that is the largest of the Patches.

In other words, if I had 3 Patch objects with Ids:

patch1.getId() = 1;
patch3.getId() = 3;
patch2.getId() = 2;

Then the number I'd like to return would be 3. At this point in time, there is no order to the Collection. However, each new Patch will always have an Id that is 1 greater than the previous, starting at 1. In other words, if I added another patch with the above, the id would be guaranteed to be 4. If I had 10 Patch objects, the largest Id would be guaranteed to be 10.

I believe something like this would work, but might cause an issue when only 1 Patch exists:

Collections.max(patches, (p1, p2) -> Long.compare(p1.getId(), p2.getId())).getId();

or

patches.stream().max((p1, p2) -> Long.compare(p1.getId(), p2.getId())).get().getId();

but both of those seem... excessive... Is there a better way of doing this?

Also, the purpose of this is to avoid casting to long. Technically, the following works, but is frowned upon:

(long) patches.size()

Sure seems like it would be awfully convenient though...

Assuming non-null values, just use Collections.max(patches, Comparator.comparing(Patch::getId)).getId();. — Savior
– Savior, Commented Apr 6, 2016 at 16:24

Paul Boddington · Accepted Answer · 2016-04-06 16:27:23Z

3

You want the id, not the Patch, so you should find the max id, not the max Patch by id.

long a = patches.stream().mapToLong(Patch::getId).max().orElse(-1);

edited Apr 6, 2016 at 16:27

answered Apr 6, 2016 at 16:24

Paul Boddington

37.8k10 gold badges69 silver badges120 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

fge Over a year ago

.max().getAsLong() :p .max() returns an OptionalLong

Jean-François Savard Over a year ago

@fge .getAsLong() :p

Paul Boddington Over a year ago

I went for orElse. When I use get() or getAsLong() people downvote.

user2869231 Over a year ago

awesome, thanks! Something to note is that, if going the get() route, I think you have to use getAsLong()?

Paul Boddington Over a year ago

Yes you do, sorry. When I said get I meant Optional.get().

Collectives™ on Stack Overflow

Get the largest attribute value in a Collection of Objects in Java

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related