2nd/10_Wiki/Dev/Topic_Java/Java_Print_Variables.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-print-variables	Java Print Variables	Programming_Language	draft	conceptual		자바 변수 출력		B	0.9	2026-07-04	2026-07-04			java programming w3schools variables concatenation	https://www.w3schools.com/python/python_variables_output.asp https://www.w3schools.com/java/java_variables_print.asp

Java Print Variables

🎯 한 줄 통찰 (One-line insight)

The + operator is dangerously overloaded — without parentheses, "The sum is " + x + y concatenates left-to-right as strings ("56"), while "The sum is " + (x + y) forces numeric addition first (11) — the exact same expression differing only in parenthesization. [S1]

🧠 핵심 개념 (Core concepts)

• + for display — combines text and a variable: "Hello " + name. [S1]
• + on two variables — concatenates or adds depending on type. [S1]
• + dual meaning — string concatenation for text, arithmetic addition for numbers. [S1]
• Left-to-right evaluation without parentheses — mixing string and numeric + operands evaluates strictly left to right, so once a string appears, everything after becomes string concatenation. [S1]
• Parentheses force numeric evaluation first — (x + y) computes the sum before concatenating with the string. [S1]

🧩 추출된 패턴 (Extracted patterns)

• The "sum is " + x + y footgun — this is a well-known Java gotcha: without parentheses around x + y, the output silently becomes string concatenation ("56") instead of the intended numeric sum ("11"), with no compiler warning. [S1]

📖 세부 내용 (Details)

• Text + variable: String name = "John"; System.out.println("Hello " + name);. [S1]
• Variable + variable (string concat): String fullName = firstName + lastName;. [S1]
• Numeric addition: int x = 5; int y = 6; System.out.println(x + y); // 11. [S1]
• Mixing footgun: System.out.println("The sum is " + x + y); // "The sum is 56" vs. System.out.println("The sum is " + (x + y)); // "The sum is 11". [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음. 괄호 유무로 인한 결과 차이가 소스에서 직접 경고됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 텍스트와 숫자를 함께 출력할 때 항상 괄호로 연산 순서를 명시하는 습관이 필요하다. [S1]

💻 코드 패턴 (Code patterns)

The parenthesization footgun (Java):

int x = 5;
int y = 6;
System.out.println("The sum is " + x + y);   // "The sum is 56"
System.out.println("The sum is " + (x + y)); // "The sum is 11"

✅ 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 Variables, Java Strings Concat, Java Strings Numbers
• 참조 맥락: + 연산자의 이중 의미(연결/덧셈)를 다루는 핵심 문서 — 괄호로 순서를 명시하는 습관이 중요하다.

📚 출처 (Sources)

• [S1] W3Schools — Java Print Variables — https://www.w3schools.com/java/java_variables_print.asp

📝 변경 이력 (Change history)

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