Intersection of two sets

Question

Is easy way to get the intersection of two sets? I have:

    Set<Long> set1 = {1,2,3}
    Set<Long> set2 = {2,3,4}

And I looking or method like:

    Set<Long> intersection = new HashSet<>();
    intersection.intersect(set1, set2);

And intersection.toString() produce me set contains {2,3}

If you don't mind to use apache commons. Here you are: https://commons.apache.org/proper/commons-collections/javadocs/api-3.2.1/org/apache/commons/collections/CollectionUtils.html#intersection(java.util.Collection, java.util.Collection) util method is called intersection — Mirek Surma, Jul 14 '15 at 09:08

score 3 · Answer 1 · answered Jul 14 '15 at 09:07

3

Note that this will modify one of the collections so you might want to create a copy first.

answered Jul 14 '15 at 09:07

xp500

score 2 · Answer 2 · answered Jul 14 '15 at 09:18

Use the retainAll() method of Set

Set<String> s1;
Set<String> s2;
s1.retainAll(s2); // s1 now contains only elements in both sets

But, retainAll, will modify the content of s1. You should create a copy of s1 and use retainAll on the copy

Avoid this by below,

Set<String> mySet = new HashSet<String>(s1); // use the copy constructor
mySet.retainAll(s2);

VWeber · Answer 3 · 2015-07-14T10:55:28.250

1

Or to preserve the values:

Set<String> intersection = new HashSet<String>(set1);
intersection.retainAll(set2);

edited Jul 14 '15 at 10:55

answered Jul 14 '15 at 09:08

VWeber

SatyaTNV · Answer 4 · 2015-07-14T09:18:33.020

1

The retainAll() method is used to remove it's elements from a list that are not contained in the specified collection.

Set<Long> set1 = {1,2,3}
Set<Long> set2 = {2,3,4}    
set1.retainAll(set2);//finally prints 2,3

edited Jul 14 '15 at 09:18

answered Jul 14 '15 at 09:12

SatyaTNV

4 Answers4