Java AbstractSet.add() is a method in the Java AbstractSet class that adds the specified element to the set, if it is not already present. It ensures that the set contains unique elements. Introduced in Java 1997 with Java 1.2, add() is commonly used to insert elements into sets, which automatically handle uniqueness for operations like filtering duplicates.

https://docs.oracle.com/javase/8/docs/api/java/util/AbstractSet.html