2nd/10_Wiki/Dev/Topic_Java/Java_TreeMap.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-treemap	Java TreeMap	Programming_Language	draft	conceptual		자바 TreeMap		B	0.89	2026-07-04	2026-07-04			java programming w3schools collections-framework treemap	https://www.w3schools.com/java/java_treemap.asp

Java TreeMap

🎯 한 줄 통찰 (One-line insight)

TreeMap's comparison table reveals a subtle constraint beyond sorting/speed — HashMap allows exactly ONE null key, while TreeMap disallows null keys entirely, since sorting requires comparing keys and null has no natural ordering position. [S1]

🧠 핵심 개념 (Core concepts)

• TreeMap — stores key-value pairs sorted automatically by key. [S1]
• Same API as HashMap — put(), get(), remove(), clear(), size(), keySet(), values(). [S1]
• No null keys — unlike HashMap (which allows one null key), TreeMap disallows null keys entirely. [S1]
• Performance trade-off — slower than HashMap due to maintaining sort order. [S1]

📖 세부 내용 (Details)

• Sorted-by-key output: TreeMap<String, String> capitalCities = new TreeMap<>(); capitalCities.put("England", "London"); capitalCities.put("Austria", "Wien"); ... // {Austria=Wien, England=London, India=New Dehli, Norway=Oslo, USA=Washington DC} — alphabetically sorted by key. [S1]
• Comparison table: HashMap (no order, allows one null key, faster) vs. TreeMap (sorted by keys, no null keys, slower). [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• null 키 제약: HashMap은 null 키를 하나 허용하지만 TreeMap은 전혀 허용하지 않는다는 점이 비교표에서 명확히 구분됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 알파벳순으로 정렬된 국가-수도 목록이 키 기반 정렬 조회의 대표 사례다. [S1]

💻 코드 패턴 (Code patterns)

TreeMap sorts entries alphabetically by key (Java):

TreeMap<String, String> capitalCities = new TreeMap<>();
capitalCities.put("England", "London");
capitalCities.put("Austria", "Wien");
capitalCities.put("India", "New Dehli");
System.out.println(capitalCities);
// {Austria=Wien, England=London, India=New Dehli}

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.89
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: Java Tutorial
• 관련 개념: Java HashMap, Java LinkedHashMap, Java TreeSet
• 참조 맥락: 정렬이 필요한 Map 구현체 — LinkedHashMap(삽입 순서 보존) 챕터로 이어짐.

📚 출처 (Sources)

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

📝 변경 이력 (Change history)

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