TreeSet
TreeSet is an ordered collection based on red-black tree implementations, and elements cannot be null. The most important feature of TreeSet is orderliness. The data stored in TreeSet is sorted.
HashSet
A HashSet is a collection of Hash table implementations that store data identified by hashCode. Data can be null, but only one.
The binary tree is traversed during TreeSet query, and the order of the binary tree is maintained when insertion and deletion are performed. Every time a HashSet accesses data, it hashes, and the performance of a HashSet is usually due to a TreeSet. Quick query to scenarios using HashSet and TreeSet when data needs to be kept in order.