Apa iku lambda lan antarmuka fungsional?

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**Lambda** (Java 8+) iku fungsi anonim sing ringkas, lan **antarmuka fungsional** iku antarmuka kanthi persis **siji metode abstrak** — jenis target sing digaweke lambda. Bareng-bareng, dheweke mawa pemrograman fungsional menyang Java lan dadi daya Stream API. ## Apa mulane penting ```java @FunctionalInterface // optional annotation — enforces ONE abstract method interface Calculator { int calculate(int a, int b); // the single abstract method } ``` Antarmuka kanthi siji metode abstrak iku "fungsional" — lambda bisa ngimplementasiake, amarga ora ana kekarepan babagan metode apa sing diwakili lambda. ## Sintaks lambda — ngimplementasiake kanthi ringkas ```java // ❌ verbose anonymous class (pre-Java 8) Calculator add = new Calculator() { public int calculate(int a, int b) { return a + b; } }; // ✅ lambda — same thing, far less boilerplate Calculator add = (a, b) -> a + b; Calculator multiply = (a, b) -> a * b; add.calculate(2, 3); // 5 ``` Lambda `(a, b) -> a + b` menehi implementasi siji metode — ora ana kelas, ora ana boilerplate tandha tangan metode. ## Antarmuka fungsional sing wis ana (java.util.function) ```java Function length = s -> s.length(); // takes T, returns R Predicate isPositive = n -> n > 0; // takes T, returns boolean Consumer printer = s -> System.out.println(s); // takes T, returns void Supplier greeting = () -> "Hello"; // takes nothing, returns T BiFunction sum = (a, b) -> a + b; // two args ``` Java menehi antarmuka fungsional sing wis disiapake kanggo bentuk-bentuk umum, digunakake ing kabeh pustaka standar (utamane stream). ## Referensi metode — luwih ringkas ```java // when a lambda just calls an existing method, use a method reference list.forEach(System.out::println); // instead of x -> System.out.println(x) list.stream().map(String::toUpperCase); // instead of s -> s.toUpperCase() list.stream().map(Integer::parseInt); // static method ref ``` ## Ngendi lambda bersinar ```java // passing behavior as arguments — the core enabler of the Stream API people.stream() .filter(p -> p.getAge() > 18) // Predicate lambda .map(Person::getName) // method reference .forEach(System.out::println); // Consumer list.sort((a, b) -> a.compareTo(b)); // Comparator lambda button.addActionListener(e -> handleClick()); // event handler ``` ## Apa mulane penting Lambda lan antarmuka fungsional mawa pemrograman fungsional menyang Java, ngowahi kanthi fundamental carane Java modern ditulis. Dheweke ngilangake boilerplate kelas anonim sing verbose kanggo ngirim **perilaku minangka data**, ngaktifake penanganan acara sing ringkas, pembanding, balikan, lan — sing paling penting — kabeh **Stream API** (sing gumantung pada lambda kanggo operasi filter/map/reduce). Pamahaman yen lambda ngarahake antarmuka fungsional (siji metode abstrak), antarmuka sing wis ana (Function, Predicate, Consumer, Supplier), lan referensi metode iku penting kanggo nulis Java modern idiomatic lan nggunakake stream, koleksi, lan API compete kanthi efektif. Dheweke nggambarake evolusi utama saka basa lan inti kanggo kelancaran Java saiki.