2nd/10_Wiki/Dev/Topic_Java/Java_ArrayList.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-arraylist	Java ArrayList	Programming_Language	draft	conceptual		자바 ArrayList		B	0.9	2026-07-04	2026-07-04			java programming w3schools collections-framework arraylist	https://www.w3schools.com/java/java_arraylist.asp

Java ArrayList

🎯 한 줄 통찰 (One-line insight)

Storing primitives in an ArrayList requires their WRAPPER classes, not the primitives themselves — ArrayList<Integer> works but ArrayList<int> doesn't compile, because ArrayList elements are objects and Java's primitives (int, boolean, char, double) aren't objects; each has an object wrapper (Integer, Boolean, Character, Double). [S1]

🧠 핵심 개념 (Core concepts)

• ArrayList — a resizable array; unlike plain arrays, elements can be added/removed at any time. [S1]
• Core methods — add(), add(index, value) (insert at position), get(), set(), remove(), clear(), size(). [S1]
• Wrapper classes required for primitives — Integer for int, Boolean for boolean, Character for char, Double for double. [S1]
• Collections.sort() — sorts an ArrayList alphabetically (Strings) or numerically (numbers). [S1]
• var keyword (Java 10+) — infers the type, avoiding repeating ArrayList<String> on both sides. [S1]
• List-typed variable holding an ArrayList — List<String> cars = new ArrayList<>(); — valid since ArrayList implements List; offers flexibility to swap implementations later. [S1]

📖 세부 내용 (Details)

• Basic creation and add: ArrayList<String> cars = new ArrayList<String>(); cars.add("Volvo"); cars.add("BMW");. [S1]
• Insert at index: cars.add(0, "Mazda"); // insert at the beginning. [S1]
• Access/modify/remove: cars.get(0); cars.set(0, "Opel"); cars.remove(0); cars.clear(); cars.size();. [S1]
• Loop with index or for-each: for (int i = 0; i < cars.size(); i++) { System.out.println(cars.get(i)); } or for (String i : cars) { System.out.println(i); }. [S1]
• Wrapper class for numbers: ArrayList<Integer> myNumbers = new ArrayList<Integer>(); myNumbers.add(10);. [S1]
• Sorting: Collections.sort(cars); // alphabetical or numeric sort. [S1]
• var keyword: var cars = new ArrayList<String>();. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 원시 타입 저장 불가: ArrayList의 요소는 객체이므로 int/boolean 등 원시 타입은 직접 저장할 수 없고 반드시 래퍼 클래스(Integer, Boolean 등)를 사용해야 함이 명시됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 문자열/숫자 리스트를 Collections.sort()로 정렬하는 것이 실전에서 자주 쓰이는 패턴이다. [S1]

💻 코드 패턴 (Code patterns)

Sorting an ArrayList with Collections.sort() (Java):

import java.util.ArrayList;
import java.util.Collections;

ArrayList<String> cars = new ArrayList<String>();
cars.add("Volvo");
cars.add("BMW");
cars.add("Ford");
cars.add("Mazda");
Collections.sort(cars);
for (String i : cars) {
    System.out.println(i);
}

✅ 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 List, Java LinkedList, Java Sort List, Java Var Keyword
• 참조 맥락: List 인터페이스의 대표 구현체 — LinkedList와의 비교 챕터로 이어짐.

📚 출처 (Sources)

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

📝 변경 이력 (Change history)

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