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78 lines
3.8 KiB
Markdown
78 lines
3.8 KiB
Markdown
---
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id: java-generics
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title: "Java Generics"
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category: "Programming_Language"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["자바 제네릭"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.9
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created_at: 2026-07-04
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updated_at: 2026-07-04
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review_reason: ""
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merge_history: []
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tags: ["java", "programming", "w3schools", "generics"]
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raw_sources: ["https://www.w3schools.com/java/java_generics.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[Java Generics]]
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## 🎯 한 줄 통찰 (One-line insight)
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`<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]
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## 🧠 핵심 개념 (Core concepts)
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- **Generics** — write classes/interfaces/methods that work across data types without fixing the type in advance. [S1]
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- **Benefits** — code reusability (one class/method, many types), type safety (compile-time error catching), cleaner code (no manual casting). [S1]
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- **Type parameter `<T>`** — a placeholder; becomes concrete (String, Integer, etc.) at usage site. [S1]
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- **Generic class** — `class Box<T> { T value; ... }`. [S1]
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- **Generic method** — `public static <T> void printArray(T[] array) { ... }`. [S1]
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- **Bounded types** — `<T extends Number>` restricts T to Number subclasses, enabling numeric methods like `.doubleValue()` inside the class body. [S1]
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- **Used internally by Collections** — `ArrayList<String>`, `HashMap<K,V>` are themselves generic. [S1]
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## 📖 세부 내용 (Details)
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- 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]
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- Generic method: `public static <T> void printArray(T[] array) { for (T item : array) { System.out.println(item); } } ... printArray(names); printArray(numbers);`. [S1]
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- 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]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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소스에서 모순되는 정보는 발견되지 않음.
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## 🛠️ 적용 사례 (Applied in summary)
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현재 발견된 실제 적용 사례가 없습니다 — Integer/Double 배열 모두에 동작하는 평균 계산(Stats<T extends Number>)이 경계 제네릭의 대표 실전 사례다. [S1]
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## 💻 코드 패턴 (Code patterns)
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Bounded generic class computing average for any Number subtype (Java):
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```java
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class Stats<T extends Number> {
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T[] nums;
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Stats(T[] nums) { this.nums = nums; }
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double average() {
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double sum = 0;
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for (T num : nums) { sum += num.doubleValue(); }
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return sum / nums.length;
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}
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}
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```
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.90
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[Java Tutorial]]
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- **관련 개념:** [[Java Wrapper Classes]], [[Java ArrayList]], [[Java Annotations]]
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- **참조 맥락:** 타입 안전한 재사용 가능 코드 — Annotations 챕터로 이어짐.
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## 📚 출처 (Sources)
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- [S1] W3Schools — Java Generics — https://www.w3schools.com/java/java_generics.asp
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## 📝 변경 이력 (Change history)
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- 2026-07-04: Initial draft synthesized from the W3Schools "Java Generics" page (Astra wiki-curation, P-Reinforce v3.1 format).
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