How to use Guava to check if every element in a collection are equal to each other

Question

Is there a simple way to use Guava to check if my Collection contains the same elements?

Check this answer http://stackoverflow.com/questions/12242083/remove-duplicates-from-list-using-guava — Ugur Artun, Feb 05 '15 at 14:09
Your 4 best alternatives are listed in this answer: http://stackoverflow.com/a/29288616/276052 — aioobe, Apr 06 '17 at 06:31

Konstantin Yovkov · Accepted Answer · 2015-02-05T14:13:23.377

2

I don't think you need Guava for that. You can simply pass all the objects from the Collection into a Set and if you result with a Set of size 1, then all the objects from the Collection will be considered as equal (because, as per definition, a Set cannot contain duplicates). For example:

public boolean checkCollectionForEqualObjects(Collection<SomeObject> collection) {
    Set<SomeObject> set = new HashSet<>();
    for (SomeObject object : collection) {
       set.add(object);
    }
    return set.size() == 1;
}

Even better, as @blgt suggested, the HashSet class has a constructor with a Collection parameter, so you can just do:

public boolean checkCollectionForEqualObjects(Collection<SomeObject> collection) {
    return new HashSet<>(collection).size() == 1;
}

edited Feb 05 '15 at 14:13

answered Feb 05 '15 at 14:08

Konstantin Yovkov

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`HashSet` has a constructor can take a `Collection` as an argument, so you don't need to do the iteration yourself – blgt Feb 05 '15 at 14:11
Thanks, @blgt. I'll add that to the answer. – Konstantin Yovkov Feb 05 '15 at 14:12

How to use Guava to check if every element in a collection are equal to each other

1 Answers1