ConcurrentHashSet in Java from ConcurrentHashMap

While you do have a ConcurrentHashMap class in Java, there is no ConcurrentHashSet.
Solution
You can easily get a ConcurrentHashSet with the following code -

Collections.newSetFromMap(new ConcurrentHashMap<Object,Boolean>())
Notes

• A Set lends itself to implementation via a Map if you think about it. So can actually just use a Map. But that may not fit in well with the context of your use.
• The HashSet class internally uses a HashMap.
• The ConcurrentHashSet obtained via the method inherits pretty much all the concurrency features of the underlying collection.
• See api-docs for newSetFromMap