Duplicate elements are not allowed: a set collection cannot contain duplicate elements, with each element appearing at most once in the set.
Unordered: The elements in a set collection are not in any particular order and are not sorted according to the order in which they were inserted.
Most implementations of sets are based on hash tables, such as HashSet and LinkedHashSet, allowing for fast element lookups and insertions.
The elements in a set are unique: each element can only appear once in a set collection.
Allowing null elements: a set collection can contain null elements, but it can only contain one null element.
The order of elements is not guaranteed: The elements in a set collection are not guaranteed to be stored in a specific order, as the specific order depends on the particular implementation class.
