I’m studying for Java SE 17 certification and I noticed already how much I need to memorize, but I don’t like to memorize… Here is my try to remember the interfaces of java collections. I may update or not if I remember…
Array → ArrayList, ArrayDeque
- Pattern: Direct array backing
- Implication: Fast random access, resizing overhead
Hash → HashMap, HashSet, LinkedHashMap, LinkedHashSet
- Pattern: Hash table + bucket array
- Implication: O(1) average operations, no ordering guarantees (except Linked*)
Linked → LinkedList, LinkedHashMap, LinkedHashSet
- Pattern: Doubly-linked list structure
- Implication: Maintains insertion/access order, sequential access
Sorted → SortedMap, SortedSet
- Pattern: Interface for natural ordering
- Implication: Elements kept in sorted order
Navigable → NavigableMap, NavigableSet
- Pattern: interfaces with Sorted + navigation methods (extends Sorted*)
- Key methods:
lowerKey(),higherKey(),floorKey(),ceilingKey() - Mental model: “Find me the closest element to X”
Tree → TreeMap, TreeSet
- Pattern: Red-black tree implementing Navigable*
- Implication: O(log n) operations, sorted + navigable
Blocking → BlockingQueue, BlockingDeque
- Pattern: interfaces for Queue + thread coordination
- Implication:
put()blocks when full,take()blocks when empty
Transfer → TransferQueue
- Pattern: interface Blocking + producer-consumer handoff
- Bonus:
transfer()waits for consumer to receive
Concurrent → ConcurrentHashMap, ConcurrentSkipListMap
- Pattern: Thread-safe without external synchronization
- Implication: Higher overhead, but no
Collections.synchronizedX()needed