Similarities Between HashSet and TreeSet

	Behavior
Unique Elements	Since HashSet and TreeSet both implements Set interface. Both are allowed to store only unique elements in their objects.
Not Thread Safe	Both implementations are not synchronized. If multiple threads access a hash set/tree set concurrently, and at least one of the threads modifies the set, it must be synchronized externally.
Clone() method copy technique	Both HashSet and TreeSet uses shallow copy technique to create a clone of  their objects.
Fail-fast Iterators	The iterators returned by this class's  method are fail-fast: if the set is modified at any time after the iterator is  created, in any way except through the iterator's own  remove method, the iterator will throw a  ConcurrentModificationException.