Java TreeSet

The Collection Framework provides two general-purpose implementations of the set interface; 
(i)HashSet 
(ii)TreeSet 
They are available in the java.util package.

TreeSet stores objects in a sorted manner. It stores its elements in a tree and they are automatically arranged in a sorted order. 

It lets you access the elements in your collection by key, or sequentially by key. 
The TreeSet implementations are useful when the developers need to extract elements from a collection in a sorted manner. 
TreeSet is not synchronized i.e. if more than one thread wants to access it at the same time then it must be synchronized externally.

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