Classical set operations for java.util.Collection

Question

Is there any built-in functionality for classical set operations on the java.util.Collection class? My specific implementation would be for ArrayList, but this sounds like s

Answer 1

Intersection is done with Collection.retainAll; subtraction with Collection.removeAll; union with Collection.addAll. In each case, as Set will act like a set and a List will act like a list.

As mutable objects, they operate in place. You'll need to explicitly copy if you want to retain the original mutable object unmutated.

Answer 2

Are you looking for java.util.Set interface (and its implementations HashSet and TreeSet (sorted))?
The interface defines removeAll(Collection c) which looks like substract(), and retainAll(Collection c) which looks like intersection.

Answer 3

I would recommend Google Guava. The Sets class seems to have exactly what you are looking for. It has a intersection method and a difference method.

This presentation is probably something you want to watch if you're interested. It refers to Google Collections, which was Guava's original name.

Answer 4

For mutable operations see accepted answer.

For an imutable variant you can do this with java 8

subtraction

set1
  .stream()
  .filter(item-> !set2.contains(item))
  .collect(Collectors.toSet())

intersection

set1
  .stream()
  .filter(item-> set2.contains(item))
  .collect(Collectors.toSet())