docs(10_Wiki): Topic_Business/General/Graphic/Programming을 Topics/ 하위로 이동

최상위 10_Wiki/Topic_*였던 4개 카테고리 폴더를 10_Wiki/Topics/Topic_* 로 재배치. 콘텐츠 변경 없음(순수 폴더 이동) — Topics/ 하위 나머지 폴더는 이미 지난 커밋에서 전부 정리된 상태(잔존 항목은 에이전트 운영 상태 및 사용자가 보존을 요청한 업데이트0615/무제 3.canvas 뿐).
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+---
+id: java-hashset
+title: "Java HashSet"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["자바 HashSet"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.9
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["java", "programming", "w3schools", "collections-framework", "hashset"]
+raw_sources: ["https://www.w3schools.com/java/java_hashset.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[Java HashSet]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+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]
+
+## 🧠 핵심 개념 (Core concepts)
+- **`HashSet`** — a Set implementation where every element is unique; implements the `Set` interface. [S1]
+- **Duplicate handling** — adding an already-present element is silently a no-op (no error, no duplicate). [S1]
+- **`contains()`** — membership test. [S1]
+- **Wrapper classes for primitives** — same rule as ArrayList: `Integer` for int, etc. [S1]
+- **`var` keyword and Set-typed variable** — same patterns as List (`var cars = new HashSet<String>();`, `Set<String> cars = new HashSet<>();`). [S1]
+
+## 📖 세부 내용 (Details)
+- Duplicate ignored: `cars.add("BMW"); cars.add("BMW"); // only appears once`. [S1]
+- 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]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+소스에서 모순되는 정보는 발견되지 않음.
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — 1~10 범위 내 값의 존재 여부를 검사하는 예제가 HashSet의 빠른 조회 특성을 보여주는 대표 사례다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Fast membership check across a range with HashSet (Java):
+```java
+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 {
+        System.out.println(i + " was not found in the set.");
+    }
+}
+```
+
+## ✅ 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 Set]], [[Java TreeSet]], [[Java LinkedHashSet]], [[Java ArrayList]]
+- **참조 맥락:** Set의 대표 구현체 — 정렬된 TreeSet 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — Java HashSet — https://www.w3schools.com/java/java_hashset.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "Java HashSet" page (Astra wiki-curation, P-Reinforce v3.1 format).