Let’s say you have a list of Duplicate (and non-duplicate) items, and you want a new collection with only the duplicate items in there. The easiest way is to extend the
HashSet
.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | public class DuplicatesOnlySet extends HashSet { private final Set new HashSet public DuplicatesOnlySet(Collection extends E> c) { super .addAll(c); } @Override public
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