Quick Answer
Main collection interfaces: Collection (root), List (ordered, duplicates allowed - ArrayList, LinkedList), Set (no duplicates - HashSet, TreeSet, LinkedHashSet), Map (key-value - HashMap, TreeMap, LinkedHashMap), Queue (FIFO - LinkedList, PriorityQueue), Deque (double-ended queue). Program to interfaces (List not ArrayList) for flexibility to swap implementations.
Answer
List: Ordered collection allowing duplicates. Set: No duplicates, unordered or sorted. Map: Key-value pairs with unique keys. Queue/Deque: FIFO or double-ended structures. Iterable: Base interface enabling iteration.
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Verified Answer
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