How to compare two hashsets ?

[Vince Hon]

I have two HashSets,
e.g. hs_1, hs_2
I want to compare these 2 hashsets to produce a new one so that hs_1 will not contain elements of hs_2
Are there any efficient method to do this ?
Thanks

[Peter den Haan]

The compact way:

Set result = new HashSet(hs_1);
reslt.removeAll(hs_2);

The efficient way:

Set result = new HashSet(hs_1.size());
for (Iterator i = hs_1.iterator(); i.hasNext(); ) {
   Object element = i.next();
   if (!hs_2.contains(element)) result.add(element);
}

Alternatively, you can just let others worry about things by using the Jakarta Commons Collections:

Collection result = CollectionUtils.subtract(hs_1, hs_2);

Hope this helps
- Peter