Set of the collection interface

The set interface and its implementation class HashSet:

• The set interface is a sub-interface of the collection interface.
• Set is an unordered and non-repeatable set of elements
• HashSet (hash set): Is an important implementation class of Set
• Set inherits the method of adding and removing from the collection interface, but it does not have a set method because the data he stored is unordered, so it cannot be given an index to modify the value of the index.
• Data traversal in set can only be traversed with a for each or an iterator. (Because the data it stores is unordered)
• The data in set is not repeatable, no matter how many times it is added, eventually only one reference to that object is retained, and the last one added is retained.
• Set can add empty object null.

Set of the collection interface