Java collections expose operations such as positional access, membership, key lookup, and endpoint removal; their implementations have different traversal and storage costs.
Choose the question first
Use a List for ordered values, a Set for membership, a Map for a key-to-value association, or a Deque for endpoint work. Map is part of the collections framework but is not a subtype of Collection.
Ordering is a contract
TreeMap orders keys. LinkedHashMap keeps encounter order. PriorityQueue orders removals but does not supply sorted iteration. Those guarantees answer different questions.
Common Mistakes
Do not choose LinkedList simply because the workload inserts elements: finding an insertion position can dominate the edit. Count traversal, copying, allocation, and synchronisation needs before selecting an implementation.