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77 lines
3.4 KiB
Markdown
77 lines
3.4 KiB
Markdown
---
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id: java-hashset
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title: "Java HashSet"
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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 HashSet"]
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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", "collections-framework", "hashset"]
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raw_sources: ["https://www.w3schools.com/java/java_hashset.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[Java HashSet]]
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## 🎯 한 줄 통찰 (One-line insight)
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Checking `numbers.contains(i)` for every value 1-10 against a HashSet with only {4, 7, 8} added demonstrates that HashSet's real strength is O(1)-style membership testing across a range — this "presence check across a range" pattern is a distinctly Set-shaped use case that ArrayList's linear `contains()` scan doesn't showcase as naturally. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **`HashSet`** — a Set implementation where every element is unique; implements the `Set` interface. [S1]
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- **Duplicate handling** — adding an already-present element is silently a no-op (no error, no duplicate). [S1]
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- **`contains()`** — membership test. [S1]
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- **Wrapper classes for primitives** — same rule as ArrayList: `Integer` for int, etc. [S1]
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- **`var` keyword and Set-typed variable** — same patterns as List (`var cars = new HashSet<String>();`, `Set<String> cars = new HashSet<>();`). [S1]
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## 📖 세부 내용 (Details)
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- Duplicate ignored: `cars.add("BMW"); cars.add("BMW"); // only appears once`. [S1]
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- Membership test across a range: `HashSet<Integer> numbers = new HashSet<Integer>(); numbers.add(4); numbers.add(7); numbers.add(8); for (int i = 1; i <= 10; i++) { if (numbers.contains(i)) { System.out.println(i + " was found in the set."); } else {...} }`. [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 — 1~10 범위 내 값의 존재 여부를 검사하는 예제가 HashSet의 빠른 조회 특성을 보여주는 대표 사례다. [S1]
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## 💻 코드 패턴 (Code patterns)
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Fast membership check across a range with HashSet (Java):
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```java
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HashSet<Integer> numbers = new HashSet<Integer>();
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numbers.add(4);
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numbers.add(7);
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numbers.add(8);
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for (int i = 1; i <= 10; i++) {
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if (numbers.contains(i)) {
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System.out.println(i + " was found in the set.");
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} else {
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System.out.println(i + " was not found in the set.");
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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 Set]], [[Java TreeSet]], [[Java LinkedHashSet]], [[Java ArrayList]]
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- **참조 맥락:** Set의 대표 구현체 — 정렬된 TreeSet 챕터로 이어짐.
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## 📚 출처 (Sources)
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- [S1] W3Schools — Java HashSet — https://www.w3schools.com/java/java_hashset.asp
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## 📝 변경 이력 (Change history)
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- 2026-07-04: Initial draft synthesized from the W3Schools "Java HashSet" page (Astra wiki-curation, P-Reinforce v3.1 format).
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