Apa iku Stream API?

Question

Apa iku Stream API?

Accepted Answer

**Stream API** (Java 8+) ngaktifake pemrosesan koleksi ing **gaya fungsional** — panyaringan, transformasi, lan agregasi data liwat pipeline operasi, diekspresikan secara deklaratif (*apa* sing kudu ditindakake) tinimbang nganggo loop eksplisit (*cara* nindakake). ## Kenapa penting ```java // ❌ imperative — explicit loop, mutable accumulator List result = new ArrayList<>(); for (Person p : people) { if (p.getAge() >= 18) { result.add(p.getName().toUpperCase()); } } // ✅ stream — declarative pipeline, reads like a description of the transformation List result = people.stream() .filter(p -> p.getAge() >= 18) // keep adults .map(p -> p.getName().toUpperCase()) // extract + transform names .collect(Collectors.toList()); // gather into a list ``` Versi stream ngekspresake niat kanthi jelas minangka rantai operasi, tanpa loop manual utawa akumulator. ## Struktur pipeline ```text Source → Intermediate operations (lazy) → Terminal operation (triggers execution) ``` ```java stream() // source .filter(...) .map(...) // intermediate — lazy, return a new stream, chainable .collect(...) // terminal — produces a result, RUNS the pipeline ``` Operasi **intermediate** (filter, map, sorted, distinct) iku **lazy** — mbangun pipeline nanging ora ilham nganti operasi **terminal** (collect, forEach, reduce, count) matandingake. ## Operasi umum ```java list.stream() .filter(x -> x > 0) // keep matching .map(x -> x * 2) // transform each .sorted() // sort .distinct() // remove duplicates .limit(10) // take first 10 .collect(Collectors.toList()); // aggregations int sum = nums.stream().mapToInt(Integer::intValue).sum(); long count = list.stream().filter(...).count(); Optional first = people.stream().filter(...).findFirst(); boolean any = list.stream().anyMatch(x -> x > 100); // grouping (very powerful) Map> byCity = people.stream().collect(Collectors.groupingBy(Person::getCity)); ``` ## reduce — lipat menyang nilai tunggal ```java int total = nums.stream().reduce(0, (a, b) -> a + b); // sum via reduction ``` ## Parallel streams ```java list.parallelStream().filter(...).collect(...); // process across multiple cores // ⚠️ use only for large data + independent/stateless operations; measure first ``` ## Kenapa penting Stream API ngowahi cara Java ngproses data — ngganti loop sing verbose lan rawan kesalahan kanthi pipeline deklaratif sing ringkas lan mudah dibaca kanggo panyaringan, pemetaan, penyortiran, pengelompokan, lan agregasi. Iki digunakake kanthi luas ing Java modern kanggo manipulasi data, nggawekake niat kode luwih jelas, lan nggabung karo lambda lan referensi metode kanggo gaya fungsional. Nempa model intermediate lazy / terminal eager, operasi umum (filter/map/collect/reduce/groupingBy), lan pilihan parallel streams (karo kawise-wisene) penting kanggo nulis Java modern sing idiomatis. Streams minangka paningkatan produktivitas lan topik wawancara sing kerep, ngemot karanasan kanthi praktik Java saiki.