---
id: csharp-interface
title: "C# Interface"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["interface implements C#", "IAnimal", "C# 인터페이스"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.85
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["csharp", "programming-language", "w3schools", "oop", "interface"]
raw_sources: ["https://www.w3schools.com/cs/cs_interface.php"]
applied_in: []
github_commit: ""
---

# [[CSharp Interface]]

## 🎯 한 줄 통찰 (One-line insight)
The tutorial states outright why interfaces exist at all: "C# does not support 'multiple inheritance' (a class can only inherit from ONE base class)" — a hard restriction with NO equivalent in Topic_CPP, where C++ freely supports true multiple class inheritance (`class Derived : public Base1, public Base2`, already documented in `[[CPP Inheritance Multiple]]`) — so C# compensates by letting a class implement MANY interfaces via the SAME `:` syntax used for single-class inheritance, making interfaces less a stylistic alternative to abstract classes and more a structural workaround for a capability C# deliberately doesn't offer at the class level. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Interface** — a "completely abstract class" containing ONLY abstract methods and properties with empty bodies; no fields/variables allowed. [S1]
- **Naming convention** — interfaces are conventionally prefixed with `I` (e.g. `IAnimal`) to distinguish them from ordinary classes at a glance. [S1]
- **Default member modifiers** — interface members are implicitly `abstract` AND `public`, with no need to write those keywords. [S1]
- **Implementation via `:`** — the SAME symbol used for inheritance; a class "implements" an interface using `:`, and must provide bodies for ALL the interface's methods. [S1]
- **No `override` keyword needed** — unlike overriding a `virtual` base method, implementing an interface method requires no `override` keyword at all. [S1]
- **Cannot instantiate an interface directly** — like an abstract class, an interface can never be `new`'d into an object. [S1]
- **No constructors** — an interface cannot have a constructor, since it can never be instantiated. [S1]
- **Motivation #2, stated explicitly** — because C# disallows multiple class inheritance, interfaces are the mechanism for achieving multiple-inheritance-like behavior (a class implementing several interfaces). [S1]

## 📖 세부 내용 (Details)
- Interface declaration: `interface Animal { void animalSound(); void run(); }` — both methods bodyless. [S1]
- Implementation: `interface IAnimal { void animalSound(); } class Pig : IAnimal { public void animalSound() { Console.WriteLine("The pig says: wee wee"); } } ... Pig myPig = new Pig(); myPig.animalSound();`. [S1]
- Explicit note that `IAnimal myObj = new IAnimal();` would be impossible, mirroring the abstract class restriction. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **다중 상속 부재를 인터페이스로 보완함**: C++는 `class Derived : public Base1, public Base2`처럼 여러 클래스를 동시에 상속하는 진짜 다중 상속을 지원했지만(`[[CPP Inheritance Multiple]]`), C#은 클래스 단위 다중 상속을 아예 지원하지 않고 대신 여러 인터페이스를 구현(implement)하는 방식으로 유사한 효과를 낸다는 점이 원문에서 직접 그 이유로 명시됨. [S1]
- **인터페이스 구현에는 override가 필요 없음**: Abstract 챕터에서 abstract 클래스를 상속할 때는 override 키워드가 필수였지만, 인터페이스를 implement할 때는 override 없이 그냥 메서드를 정의하면 된다는 차이가 확인됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
IAnimal 인터페이스의 animalSound() 메서드를 Pig 클래스가 override 없이 그대로 구현해 호출하는 예제가 원문에서 직접 실전 활용 사례로 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Interface implementation — no `override` keyword required (C#):
```csharp
interface IAnimal
{
    void animalSound(); // no body
}
class Pig : IAnimal    // "implements" -- same : syntax as inheritance
{
    public void animalSound()   // no `override` needed
    {
        Console.WriteLine("The pig says: wee wee");
    }
}

Pig myPig = new Pig();
myPig.animalSound();
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.85
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[C# Tutorial]]
- **관련 개념:** [[CSharp Abstract]], [[CSharp Interface Multi]], [[CPP Inheritance Multiple]]
- **참조 맥락:** Interface 섹션 — Multiple Interfaces 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C# Interface — https://www.w3schools.com/cs/cs_interface.php

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