2nd/10_Wiki/Topics/Architecture/Object-Oriented-Programming.md

---
id: wiki-2026-0508-object-oriented-programming
title: Object-Oriented Programming (OOP)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [OOP, Object Oriented Programming, 객체지향, 객체지향 프로그래밍]
duplicate_of: none
source_trust_level: A
confidence_score: 0.95
verification_status: applied
tags: [oop, programming-paradigm, design, architecture]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: java-typescript-cpp
  framework: multi
---

# Object-Oriented Programming (OOP)

## 매 한 줄
> **"매 data + behavior를 object로 묶고, polymorphism으로 동작을 추상화하는 패러다임."**. Simula 67 (1967) → Smalltalk (1972) → C++ (1985) → Java (1995) → 매 mainstream. 2026 현재는 OO + FP hybrid가 dominant — Java records, Kotlin data class, TypeScript readonly class, Rust trait이 그 증거.

## 매 핵심

### 매 4 pillar
- **Encapsulation**: 매 internal state hide, expose behavior — `private` field + `public` method.
- **Inheritance**: 매 reuse + specialize — 단 *favor composition over inheritance* (GoF).
- **Polymorphism**: 매 same interface, different impl — virtual dispatch · duck typing.
- **Abstraction**: 매 essential 만 expose — interface · abstract class.

### 매 SOLID (Robert C. Martin)
- **S**ingle Responsibility — 매 class one reason to change.
- **O**pen/Closed — 매 extend without modify.
- **L**iskov Substitution — 매 subtype substitutable.
- **I**nterface Segregation — 매 small focused interfaces.
- **D**ependency Inversion — 매 depend on abstraction.

### 매 응용
1. Domain-Driven Design — Entity, Value Object, Aggregate.
2. GUI framework — Component hierarchy (React class component, Qt widget).
3. Game engine — Entity-Component-System (modern hybrid).

## 💻 패턴

### Encapsulation — invariant 보장
```java
public final class Money {
    private final BigDecimal amount;
    private final Currency currency;
    public Money(BigDecimal a, Currency c) {
        if (a.signum() < 0) throw new IllegalArgumentException("negative");
        this.amount = a; this.currency = c;
    }
    public Money add(Money other) {
        if (!currency.equals(other.currency))
            throw new IllegalStateException("currency mismatch");
        return new Money(amount.add(other.amount), currency);
    }
}
```

### Polymorphism — strategy
```typescript
interface Shipping {
  calculate(weight: number): number;
}
class StandardShipping implements Shipping {
  calculate(w: number) { return w * 5; }
}
class ExpressShipping implements Shipping {
  calculate(w: number) { return w * 12 + 10; }
}
function totalCost(items: Item[], shipping: Shipping): number {
  const w = items.reduce((s, i) => s + i.weight, 0);
  return items.reduce((s, i) => s + i.price, 0) + shipping.calculate(w);
}
```

### Composition over inheritance
```typescript
// BAD: deep hierarchy
class Animal {}
class Dog extends Animal {}
class FlyingDog extends Dog {} // ???

// GOOD: composition
class Animal {
  constructor(
    private mover: Movement,
    private noise: NoiseMaker,
  ) {}
  move() { return this.mover.move(); }
  speak() { return this.noise.sound(); }
}
const dog = new Animal(new Walking(), new Bark());
const bird = new Animal(new Flying(), new Chirp());
```

### Abstract class + template method
```java
public abstract class HttpHandler {
    public final Response handle(Request req) {
        if (!authenticate(req)) return Response.unauthorized();
        var data = process(req);
        return render(data);
    }
    protected abstract boolean authenticate(Request req);
    protected abstract Object process(Request req);
    protected Response render(Object data) {
        return Response.ok().json(data);
    }
}
```

### Modern hybrid — record (Java 21) / data class
```java
public record User(UserId id, Email email, String name) {
    public User {  // compact constructor
        Objects.requireNonNull(email);
        if (name.isBlank()) throw new IllegalArgumentException();
    }
    public User withName(String n) { return new User(id, email, n); }
}
```

### Trait-based OOP (Rust)
```rust
trait Drawable {
    fn draw(&self, canvas: &mut Canvas);
    fn bounds(&self) -> Rect;
}
struct Circle { center: Point, r: f32 }
impl Drawable for Circle {
    fn draw(&self, c: &mut Canvas) { c.circle(self.center, self.r); }
    fn bounds(&self) -> Rect { Rect::around(self.center, self.r) }
}
fn render_all(shapes: &[Box<dyn Drawable>], canvas: &mut Canvas) {
    for s in shapes { s.draw(canvas); }
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Domain with complex invariants | OOP + DDD entities/VO |
| Pure data transformation | FP (immutable + pure functions) |
| Plug-in / extensibility | Interface + DI |
| State machine | OOP class with explicit states |
| Hot loop, ECS scale | Data-Oriented (avoid virtual dispatch) |

**기본값**: hybrid OOP+FP — value objects immutable, services with interfaces, pure functions for transforms.

## 🔗 Graph
- 변형: [[Functional_Programming]] · [[Procedural-Architecture-Systems]] · [[ECS]]
- 응용: [[SOLID Principles]] · [[Polymorphism (다형성)]] · [[Object Seam (객체 접점)]] · [[Bounded_Context]]
- Adjacent: [[High-Cohesion-Low-Coupling]] · [[Dependency_Inversion_Principle]] · [[Hexagonal_Architecture_Ports_and_Adapters]]

## 🤖 LLM 활용
**언제**: business domain modeling, framework/library design, GUI hierarchy, plug-in architecture.
**언제 X**: hot numerical loop (DOD better), pure transform pipeline (FP cleaner), 1-file script.

## ❌ 안티패턴
- **God Object**: 매 모든 책임 한 class — SRP 위반.
- **Anemic Domain Model**: data only, behavior in service — OOP 무력화.
- **Deep inheritance (4+ levels)**: 매 fragile base class.
- **Premature interface**: 매 single impl을 interface로 — YAGNI.
- **Setter everywhere**: 매 invariant 깨짐 — immutable + factory.

## 🧪 검증 / 중복
- Verified (GoF *Design Patterns* 1994, Martin *Clean Code* 2008, Evans *DDD* 2003, Java/Kotlin/Rust 2026 docs).
- 신뢰도 A.
- Duplicates: `객체_지향_프로그래밍(OOP).md`, `객체_지향_프로그래밍_Object-Oriented_Programming,_OOP.md` should redirect here.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — canonical OOP doc (4 pillars + SOLID + modern hybrid) |