2nd/10_Wiki/Topics/Topic_Programming/Topic_Java/Java_Lambda.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
java-lambda	Java Lambda	Programming_Language	draft	conceptual		lambda expressions 자바 람다		B	0.9	2026-07-04	2026-07-04			java programming w3schools lambda functional-interface	https://www.w3schools.com/java/java_lambda.asp

Java Lambda

🎯 한 줄 통찰 (One-line insight)

A lambda can only replace an anonymous class when the target interface is "functional" (exactly ONE abstract method) — the tutorial's own rule of thumb draws the line precisely there: lambda for short single-method interfaces, anonymous class when you need multiple methods, extra fields, or to extend a class. [S1]

🧠 핵심 개념 (Core concepts)

• Lambda expression (Java 8+) — a short, nameless block of code taking parameters and returning a value. [S1]
• Syntax — parameter -> expression; multiple parameters need parentheses; complex bodies need { } + explicit return. [S1]
• Functional interface requirement — a lambda's target type must be an interface with EXACTLY one abstract method. [S1]
• Common use — passed as arguments to methods like ArrayList.forEach(). [S1]
• Built-in functional interfaces — e.g. Consumer<T> from java.util.function. [S1]
• Custom functional interfaces — user-defined single-method interfaces work as lambda targets too. [S1]
• Lambda vs. anonymous class rule of thumb — lambda for short single-method interfaces; anonymous class for multiple methods/fields/extending a class. [S1]

📖 세부 내용 (Details)

• forEach with lambda: numbers.forEach((n) -> { System.out.println(n); });. [S1]
• Lambda stored in a variable (Consumer): Consumer<Integer> method = (n) -> { System.out.println(n); }; numbers.forEach(method);. [S1]
• Lambda as method parameter (custom functional interface): interface StringFunction { String run(String str); } ... StringFunction exclaim = (s) -> s + "!"; printFormatted("Hello", exclaim);. [S1]
• Same task via anonymous class vs. lambda: Greeting g = new Greeting() { public void sayHello() {...} }; vs. Greeting g = () -> System.out.println("Hello from lambda");. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 람다 사용의 전제 조건: 대상 인터페이스가 반드시 함수형 인터페이스(추상 메서드 1개)여야 익명 클래스를 람다로 대체할 수 있다는 점이 규칙으로 명시됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — ArrayList.forEach()에 람다를 전달하는 패턴이 가장 흔한 실전 활용이다. [S1]

💻 코드 패턴 (Code patterns)

Lambda passed to forEach() (Java):

ArrayList<Integer> numbers = new ArrayList<Integer>();
numbers.add(5); numbers.add(9); numbers.add(8); numbers.add(1);
numbers.forEach((n) -> { System.out.println(n); });

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.90
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: Java Tutorial
• 관련 개념: Java Anonymous, Java Interface, Java Threads, Java Advanced Sorting
• 참조 맥락: 익명 클래스의 축약형 — 고급 정렬(Comparator 람다) 챕터로 직접 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — Java Lambda Expressions — https://www.w3schools.com/java/java_lambda.asp

📝 변경 이력 (Change history)

• 2026-07-04: Initial draft synthesized from the W3Schools "Java Lambda Expressions" page (Astra wiki-curation, P-Reinforce v3.1 format).