Set<E> other
) Returns a new set which contains all the elements of this set and other.
That is, the returned set contains all the elements of this Set and
all the elements of other.
Source
/**
* Returns a new set which contains all the elements of this set and [other].
*
* That is, the returned set contains all the elements of this [Set] and
* all the elements of [other].
*/
Set<E> union(Set<E> other);