---
id: java-inheritance
title: "Java Inheritance"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["subclass", "superclass", "extends keyword", "자바 상속"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["java", "programming", "w3schools", "oop", "inheritance"]
raw_sources: ["https://www.w3schools.com/java/java_inheritance.asp"]
applied_in: []
github_commit: ""
---

# [[Java Inheritance]]

## 🎯 한 줄 통찰 (One-line insight)
The choice between `protected` and `private` on a parent attribute directly determines whether inheritance "works" for that field — the source deliberately uses `protected` on Vehicle's `brand` and notes that `private` would have blocked Car from accessing it at all. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Subclass (child)** — the class that inherits from another. [S1]
- **Superclass (parent)** — the class being inherited from. [S1]
- **`extends`** — keyword used to inherit from a class. [S1]
- **`protected`** — required (not `private`) if a subclass needs to access a parent attribute directly. [S1]
- **`final` on a class** — prevents any class from extending it; attempting to do so is a compile error. [S1]
- **Motivation** — code reusability: inherit attributes/methods of an existing class into a new one. [S1]

## 📖 세부 내용 (Details)
- Basic inheritance: `class Vehicle { protected String brand = "Ford"; public void honk() { System.out.println("Tuut, tuut!"); } } class Car extends Vehicle { private String modelName = "Mustang"; ... } ... myCar.honk(); myCar.brand + " " + myCar.modelName;`. [S1]
- Final class blocks inheritance: `final class Vehicle { ... } class Car extends Vehicle { ... } // error: cannot inherit from final Vehicle`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **protected 필수성**: brand가 private이었다면 Car 클래스가 접근할 수 없었을 것이라는 점이 명시적으로 강조됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — Vehicle→Car 상속 구조는 다형성(Polymorphism) 챕터의 직접적 전제가 된다. [S1]

## 💻 코드 패턴 (Code patterns)
Subclass inheriting a protected attribute and a method (Java):
```java
class Vehicle {
    protected String brand = "Ford";
    public void honk() {
        System.out.println("Tuut, tuut!");
    }
}
class Car extends Vehicle {
    private String modelName = "Mustang";
    public static void main(String[] args) {
        Car myCar = new Car();
        myCar.honk();
        System.out.println(myCar.brand + " " + myCar.modelName);
    }
}
```

## ✅ 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 Modifiers]], [[Java Polymorphism]], [[Java Super Keyword]], [[Java Abstraction]]
- **참조 맥락:** 클래스 간 속성/메서드 재사용 — 다형성/super 키워드 챕터로 직접 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — Java Inheritance (Subclass and Superclass) — https://www.w3schools.com/java/java_inheritance.asp

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