2nd/10_Wiki/Topics/Domain_Programming/Topic_Java/Java_HashSet.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-hashset	Java HashSet	Programming_Language	draft	conceptual		자바 HashSet		B	0.9	2026-07-04	2026-07-04			java programming w3schools collections-framework hashset	https://www.w3schools.com/java/java_hashset.asp

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):

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).