Question

I’m wondering if there is a quick/clean way to get the symmetric difference between two sets ?

I have:

Set<String> s1 = new HashSet<String>();
s1.add("a");
s1.add("b");
s1.add("c");

Set<String> s2 = new HashSet<String>();
s2.add("b");

I need something like:

Set<String> diff = Something.diff(s1, s2);
// diff would contain ["a", "c"]

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Just to clarify I need the symmetric difference.

Answer 1

You can use some functions from the Google Guava library (which is really great, I strongly recommend it!):

Sets.difference(s1, s2);
Sets.symmetricDifference(s1, s2);

Javadocs for difference() and symmetricDifference()

symmetricDifference() does exactly what you are asking for, but difference() is also often helpful.

Both methods return a live view, but you can for example call .immutableCopy() on the resulting set to get a non-changing set. If you don’t want a view, but need a set instance you can modify, call .copyInto(s3). See SetView for these methods.