Does adding an element to a HashSet replace the existing one if it already exists?

In a HashSet, when attempting to add an element that already exists in the set, the existing element is not replaced. The add() method simply returns false, indicating that the element was not added because it already exists. Thus, the set remains unchanged.

Example in Java:

HashSet<String> set = new HashSet<>();
set.add("apple"); // returns true
boolean added = set.add("apple"); // returns false, element not added