What are the Set and TreeSet classes used for?

The Set interface in Java is used to store unique elements, meaning that duplicates are not allowed. It does not maintain any specific order of its elements. The TreeSet class, which implements the Set interface, is specifically used to store elements in a sorted order. It internally uses a red-black tree data structure to maintain the sorted order of its elements. TreeSet provides efficient operations for adding, removing, and retrieving elements, with time complexities logarithmic to the size of the set. It is commonly used when you need to store unique elements in a sorted order and perform efficient operations such as searching and traversal.