Which collection guarantees unique elements with no duplicates?

Which collection guarantees unique elements with no duplicates?

• A. List
• B. Map
• C. Queue
• D. Set

Answer: (D)

A Set is designed to hold distinct elements, ensuring each value appears at most once. When you try to add a value that’s already present, the Set simply ignores it (or indicates it was already there), so duplicates never enter the collection. This behavior is what guarantees uniqueness. In contrast, a List allows duplicates and preserves insertion order; a Queue also permits duplicates and emphasizes order and throughput; a Map stores key–value pairs where keys are unique but values can repeat, so the collection of values isn’t guaranteed to be unique.

A Set is designed to hold distinct elements, ensuring each value appears at most once. When you try to add a value that’s already present, the Set simply ignores it (or indicates it was already there), so duplicates never enter the collection. This behavior is what guarantees uniqueness.

In contrast, a List allows duplicates and preserves insertion order; a Queue also permits duplicates and emphasizes order and throughput; a Map stores key–value pairs where keys are unique but values can repeat, so the collection of values isn’t guaranteed to be unique.