2nd/10_Wiki/Dev/Topic_Java/Java_Generics.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-generics	Java Generics	Programming_Language	draft	conceptual		자바 제네릭		B	0.9	2026-07-04	2026-07-04			java programming w3schools generics	https://www.w3schools.com/java/java_generics.asp

Java Generics

🎯 한 줄 통찰 (One-line insight)

<T extends Number> bounds a generic to only numeric wrapper types specifically so .doubleValue() becomes callable inside the class — without that bound, T could be any type (including one with no doubleValue() method), so the bound isn't just a restriction, it's what makes the generic method's body compile at all. [S1]

🧠 핵심 개념 (Core concepts)

• Generics — write classes/interfaces/methods that work across data types without fixing the type in advance. [S1]
• Benefits — code reusability (one class/method, many types), type safety (compile-time error catching), cleaner code (no manual casting). [S1]
• Type parameter <T> — a placeholder; becomes concrete (String, Integer, etc.) at usage site. [S1]
• Generic class — class Box<T> { T value; ... }. [S1]
• Generic method — public static <T> void printArray(T[] array) { ... }. [S1]
• Bounded types — <T extends Number> restricts T to Number subclasses, enabling numeric methods like .doubleValue() inside the class body. [S1]
• Used internally by Collections — ArrayList<String>, HashMap<K,V> are themselves generic. [S1]

📖 세부 내용 (Details)

• Generic class: class Box<T> { T value; void set(T value) { this.value = value; } T get() { return value; } } ... Box<String> stringBox = new Box<>(); Box<Integer> intBox = new Box<>();. [S1]
• Generic method: public static <T> void printArray(T[] array) { for (T item : array) { System.out.println(item); } } ... printArray(names); printArray(numbers);. [S1]
• Bounded generic: class Stats<T extends Number> { T[] nums; double average() { double sum = 0; for (T num : nums) { sum += num.doubleValue(); } return sum / nums.length; } } — works for both Integer[] and Double[]. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — Integer/Double 배열 모두에 동작하는 평균 계산(Stats)이 경계 제네릭의 대표 실전 사례다. [S1]

💻 코드 패턴 (Code patterns)

Bounded generic class computing average for any Number subtype (Java):

class Stats<T extends Number> {
    T[] nums;
    Stats(T[] nums) { this.nums = nums; }
    double average() {
        double sum = 0;
        for (T num : nums) { sum += num.doubleValue(); }
        return sum / nums.length;
    }
}

✅ 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 Wrapper Classes, Java ArrayList, Java Annotations
• 참조 맥락: 타입 안전한 재사용 가능 코드 — Annotations 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — Java Generics — https://www.w3schools.com/java/java_generics.asp

📝 변경 이력 (Change history)

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