Stream API ni nini?

Question

Stream API ni nini?

Accepted Answer

**Stream API** (Java 8+) inaruhusu **usindikaji wa mtindo wa utendaji** wa mkusanyiko — kuchuja, kubadilisha na kuoanisha data kupitia bomba la shughuli, zilizoonyeshwa kwa kutunga (*nini* kufanya) badala ya loops zilizo wazi (*jinsi*). ## Mtindo wa amri vs Stream ```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 ``` Toleo la stream linaonyesha kusudi kwa uwazi kama mlolongo wa shughuli, bila loop ya mkono au mkusanyika. ## Muundo wa bomba ```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 ``` Shughuli za **kati** (filter, map, sorted, distinct) ni **wazimu** — zina kujenga bomba lakini hazifanyi hadi shughuli ya **kimawazo** (collect, forEach, reduce, count) kuichagiza. ## Shughuli za kawaida ```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 — kukunja hadi thamani moja ```java int total = nums.stream().reduce(0, (a, b) -> a + b); // sum via reduction ``` ## Mtiririko sambamba ```java list.parallelStream().filter(...).collect(...); // process across multiple cores // ⚠️ use only for large data + independent/stateless operations; measure first ``` ## Kwa nini inahusu Stream API ilibadilisha jinsi Java inavyosindika data — kubadilisha loops ndefu na kosa-nyeti na bomba ndogo, inayosomeka, na inayotunga kwa kuchuja, kupanga ramani, kupanga, kukamatia na kuoanisha. Inatumika sana katika Java ya kisasa kwa uongezaji wa data, hufanya kusudi la code kuwa wazi zaidi, na inajumuika na lambdas na marejeleo ya njia kwa mtindo wa utendaji. Kuelewa wazimu wa kati/kusanyika kwa haraka ya akili, shughuli za kawaida (filter/map/collect/reduce/groupingBy) na chaguo la mtiririko sambamba (na onyo zake) ni muhimu kwa kuandika Java ya kisasa ya idiomatiki. Mtiririko ni kama kuongeza uzalishaji na mada ya kawaida ya mahojiano, inayoakisi ujuzi wa shughuli za Java za sasa.