---
id: java-var-keyword
title: "Java Var Keyword"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["var (Java 10+)", "type inference", "자바 var 키워드"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["java", "programming", "w3schools", "var", "type-inference"]
raw_sources: ["https://www.w3schools.com/java/java_var.asp"]
applied_in: []
github_commit: ""
---

# [[Java Var Keyword]]

## 🎯 한 줄 통찰 (One-line insight)
`var` (Java 10+) is type INFERENCE, not dynamic typing — the compiler still locks in a fixed type at the moment of assignment (`var x = 5;` → permanently int), so `x = 9.99;` later still errors exactly as if you'd written `int x = 5;` explicitly. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`var`** (Java 10, 2018) — lets the compiler infer a variable's type from its assigned value. [S1]
- **Must assign at declaration** — `var x;` alone is an error; `var x = 5;` is required. [S1]
- **Type still locked in** — once inferred, the type cannot change, exactly like an explicit declaration. [S1]
- **Best for complex types** — most useful for verbose generic types like `ArrayList<String>`, less useful for simple types where explicit typing is already clear. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **var is sugar, not a type system change** — it removes REPETITION (`ArrayList<String> cars = new ArrayList<String>();` → `var cars = new ArrayList<String>();`) without weakening static type safety at all. [S1]

## 📖 세부 내용 (Details)
- Basic inference: `var x = 5; // x is an int`. [S1]
- Multiple types inferred: `var myNum = 5; var myDouble = 9.98; var myChar = 'D'; var myBoolean = true; var myString = "Hello";`. [S1]
- Must assign immediately: `var x; // Error` vs. `var x = 5; // OK`. [S1]
- Type stays locked: `var x = 5; x = 10; // OK; x = 9.99; // Error`. [S1]
- Reduces verbosity for complex types: `var cars = new ArrayList<String>();` instead of `ArrayList<String> cars = new ArrayList<String>();`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — ArrayList/HashMap처럼 제네릭 타입이 장황할 때 코드 가독성을 높이는 데 쓰인다. [S1]

## 💻 코드 패턴 (Code patterns)
var reduces verbosity for generic types (Java):
```java
// Without var
ArrayList<String> cars = new ArrayList<String>();
// With var
var cars = new ArrayList<String>();
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[Java Tutorial]]
- **관련 개념:** [[Java Variables]], [[Java ArrayList]], [[Java Data Types]]
- **참조 맥락:** 타입 추론으로 코드 간결화 — 여전히 정적 타이핑 안전성은 유지된다.

## 📚 출처 (Sources)
- [S1] W3Schools — Java var Keyword — https://www.w3schools.com/java/java_var.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "Java var Keyword" page (Astra wiki-curation, P-Reinforce v3.1 format).