Collections Framework iku set kesatuan interface lan kelas Java kanggo nyimpen lan ngolah klompok obyek — List, Set, Map, Queue lan implementasine. Iki nyediake struktur data sing wis rampung lan wis diuji kanthi apik, mula aku jarang banget nggawe dhewe.
Collection
├── List — ordered, allows duplicates, indexed access
├── Set — no duplicates, models uniqueness
└── Queue — FIFO/priority ordering for processing
Map (separate hierarchy) — key→value pairs
List<String> list = new ArrayList<>(); // backed by an array — fast random access
list.add("a");
list.get(0); // index access — O(1)
list.contains("a"); // O(n) search
// LinkedList — fast insert/remove at ends, O(n) random access
ArrayList (didukung array, indexing cepet) iku sing dereng; LinkedList cocok kanggo penyisipan ende sing asik.
Set<String> set = new HashSet<>(); // O(1) add/contains, NO order
set.add("a");
set.add("a"); // ignored — duplicates not allowed
set.contains("a"); // O(1) — great for membership tests
// TreeSet — sorted order; LinkedHashSet — insertion order
HashSet menehi pariksa keunikan O(1); TreeSet tetep nggawe unsur sing diurut.
Map<String, Integer> map = new HashMap<>(); // O(1) get/put, no order
map.put("age", 30);
map.get("age"); // 30
map.getOrDefault("x", 0); // safe access with default
map.computeIfAbsent("list", k -> new ArrayList<>()); // handy for grouping
// TreeMap — sorted by key; LinkedHashMap — insertion order
HashMap iku kuda tunggangan kanggo panggolekkan O(1) adhedhasar kunci.
Need ordered + indexed + duplicates → ArrayList
Need uniqueness, fast lookup → HashSet
Need key→value, fast lookup → HashMap
Need sorted order → TreeSet / TreeMap
Need FIFO processing → ArrayDeque / LinkedList (Queue)
Need thread-safety → ConcurrentHashMap, etc.
ArrayList: get O(1), add-end O(1), contains/remove O(n)
HashMap/HashSet: get/put/contains O(1) average
TreeMap/TreeSet: O(log n) (sorted)
LinkedList: add/remove-ends O(1), get O(n)
Collections Framework iku salah satu bagean sing paling digunakake saka Java — meh kabeh program nyimpen lan ngolah klompok data karo iki.
Milih koleksi sing bener iku katrampilan kunci sing langsung mengaruhi kabenaran lan performa: ArrayList kanggo data urut sing duwe indeks, HashSet kanggo keunikan, HashMap kanggo panggolekkan kunci cepet, lan varian sing diurut/bersamaan yen perlu.
Paham interface (List/Set/Map/Queue), implementasine, lan utamane karakteristik performa (panggolekkan HashMap O(1) lawan pencarian list O(n)) ngidini aku milih struktur sing pas tinimbang nggawe omong kosong sing salah (sabab umum kode sing alon).
Iki pengetahuan dasar lan praktis kanggo pengembangan Java saben hari.
Pustaka pitakon wawancara IT kanthi jawaban rinci — saka Junior nganti Senior.
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