What is the Set interface?

The Set interface in Java is your go-to when you need a collection that stores unique elements only. No duplicates, no index-based access.

-Set extends the Collection interface and lives in java.util. Its defining contract: it will never contain duplicate elements.

-Internally, "duplicate" is determined by equals() and hashCode() — so you must override both when using custom objects.

1.HashSet:

Use HashSet when you only care about uniqueness and O(1) average-case performance, and don't need a predictable iteration order.

O(1) avg -Backed by a HashMap. Fastest for add/remove/contains. No ordering guarantee whatsoever.

Example:

Set < String > fruits = new HashSet <>(); fruits . add ( "Apple" ); fruits . add ( "Mango" ); fruits .…