---
id: java-interface
title: "Java Interface"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["implements keyword", "자바 인터페이스"]
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", "interface"]
raw_sources: ["https://www.w3schools.com/java/java_interface.asp"]
applied_in: []
github_commit: ""
---

# [[Java Interface]]

## 🎯 한 줄 통찰 (One-line insight)
Interfaces exist specifically to work around Java's single-inheritance limitation — a class can only `extends` one superclass, but it can `implements` multiple interfaces (comma-separated), making interfaces Java's mechanism for something resembling multiple inheritance. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Interface** — a fully "abstract class" grouping related methods that all lack bodies. [S1]
- **`implements`** — the keyword a class uses to adopt an interface (vs. `extends` for classes). [S1]
- **Mandatory override** — implementing a class MUST override every method the interface declares. [S1]
- **Implicit modifiers** — interface methods are `abstract` + `public` by default; interface attributes are `public`, `static`, `final` by default. [S1]
- **No constructor** — interfaces cannot have constructors (can't be instantiated). [S1]
- **Multiple interfaces** — a class can implement several interfaces, separated by commas — Java's substitute for multiple inheritance. [S1]

## 📖 세부 내용 (Details)
- Interface declaration: `interface Animal { public void animalSound(); public void run(); }`. [S1]
- Implementation: `class Pig implements Animal { public void animalSound() { System.out.println("The pig says: wee wee"); } public void sleep() { System.out.println("Zzz"); } }`. [S1]
- Multiple interfaces: `class DemoClass implements FirstInterface, SecondInterface { public void myMethod() {...} public void myOtherMethod() {...} }`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **다중 상속 대안**: Java는 클래스의 다중 상속을 지원하지 않지만, 인터페이스 다중 구현으로 유사 효과를 달성한다는 점이 명시됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 여러 인터페이스를 한 클래스가 동시에 구현하는 패턴이 다중 상속의 대체 수단으로 쓰인다. [S1]

## 💻 코드 패턴 (Code patterns)
Class implementing multiple interfaces (Java):
```java
interface FirstInterface {
    public void myMethod();
}
interface SecondInterface {
    public void myOtherMethod();
}
class DemoClass implements FirstInterface, SecondInterface {
    public void myMethod() {
        System.out.println("Some text..");
    }
    public void myOtherMethod() {
        System.out.println("Some other text...");
    }
}
```

## ✅ 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 Abstraction]], [[Java Anonymous]], [[Java Enums]]
- **참조 맥락:** 다중 상속의 대안 — 익명 클래스 챕터에서 인터페이스를 즉석 구현하는 방법으로 이어짐.

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

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