Match each Java collection interface to its characteristics.
Drag a concept onto its matching description — or click a concept then click the description.
Ordered collection allowing duplicates
Collection with no duplicates
Collection for holding elements prior to processing
Key-value pairs, keys unique
Double-ended queue supporting insertion/removal at both ends
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
List: Ordered collection (also known as sequence) that allows duplicate elements.
List is ordered and allows duplicates; Set is unordered and no duplicates; Queue is FIFO order; Map maps keys to values with unique keys. Common confusions include swapping List/Set characteristics or misidentifying Map as a collection of single elements.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
List: Ordered collection (also known as sequence) that allows duplicate elements.
Why this is correct
List is defined as an ordered sequence that may contain duplicates.
Set: Collection that cannot contain duplicate elements, no specific order.
Why this is correct
Set is a collection with no duplicates and no guaranteed order.
Queue: Collection designed for holding elements prior to processing, typically FIFO order.
Why this is correct
Queue is a collection for processing elements in FIFO order.
Map: Object that maps keys to values, cannot contain duplicate keys.
Why this is correct
Map associates keys with values and does not allow duplicate keys.
Set: Ordered collection that allows duplicate elements.
Why it's wrong here
Incorrect — this describes List, not Set. Set does not allow duplicates and is unordered.
Map: Collection of elements with no order and no duplicates.
Why it's wrong here
Incorrect — this describes Set, not Map. Map has keys and values, allows duplicate values, and does not guarantee order.
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Last reviewed: Jun 11, 2026
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