2nd/10_Wiki/Topics/Programming & Language/객체 지향 프로그래밍 (Object-Oriented Programming).md

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id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-객체-지향-프로그래밍-object-oriented-prog	객체 지향 프로그래밍 (Object-Oriented Programming)	10_Wiki/Topics	verified	self	OOP Object-Oriented Programming 객체지향	none	A	0.9	applied	oop encapsulation polymorphism paradigm		2026-05-10	pending	language framework Java/TS/Python agnostic

객체 지향 프로그래밍 (Object-Oriented Programming)

매 한 줄

"매 state + behavior 를 object 로 묶어 message passing 으로 협력시키는 패러다임". Smalltalk (1972) → C++/Java → 매 modern composition-over-inheritance + interface-driven 으로 진화. 매 2026 의 OOP 는 functional core + OO shell 의 hybrid 가 dominant.

매 핵심

매 4 기둥

• Encapsulation: state 의 hide + 매 invariant 의 보호.
• Abstraction: 매 interface 만 노출 — implementation hide.
• Inheritance: 매 sub-class 의 reuse — 매 fragile base class 위험.
• Polymorphism: subtype / parametric / ad-hoc — 매 substitutability.

매 modern OOP 의 best practice

• Composition > Inheritance: 매 has-a >> is-a.
• Program to interface: 매 concrete type 의 dependency X.
• SOLID: SRP / OCP / LSP / ISP / DIP.
• Immutable by default: record / data class / value object.

매 응용

1. UI framework (React class — but hooks shifted toward functional).
2. Game engine (Unity GameObject / Component).
3. ORM entity (JPA / SQLAlchemy / Active Record).
4. GUI (Swing, Qt, AppKit).

💻 패턴

Encapsulation + invariant

public class Account {
    private long balanceCents;  // private = hidden
    public void deposit(long cents) {
        if (cents <= 0) throw new IllegalArgumentException();
        this.balanceCents += cents;
    }
    public long getBalanceCents() { return balanceCents; }
    // 매 setter 없음 — invariant 보호
}

Polymorphism (interface)

interface PaymentMethod {
  charge(amountCents: number): Promise<TxResult>;
}
class StripeCard implements PaymentMethod {
  async charge(c: number) { /* stripe sdk */ return { ok: true }; }
}
class Paypal implements PaymentMethod {
  async charge(c: number) { /* paypal sdk */ return { ok: true }; }
}
async function checkout(pm: PaymentMethod, total: number) {
  return pm.charge(total);  // 매 same call, different impl
}

Composition over Inheritance

// ❌ Inheritance hell
// class FlyingFish extends Fish, Bird {} — multiple inheritance 문제

// ✅ Composition
interface Swim { swim(): void }
interface Fly { fly(): void }
class Fish implements Swim { swim() { console.log("swim"); } }
class Bird implements Fly { fly() { console.log("fly"); } }
class FlyingFish implements Swim, Fly {
  private swimmer = new Fish();
  private flyer = new Bird();
  swim() { this.swimmer.swim(); }
  fly() { this.flyer.fly(); }
}

Strategy Pattern

from typing import Protocol
class SortStrategy(Protocol):
    def sort(self, data: list[int]) -> list[int]: ...

class QuickSort:
    def sort(self, data): return sorted(data)
class BubbleSort:
    def sort(self, data):
        d = data[:]
        for i in range(len(d)):
            for j in range(len(d)-i-1):
                if d[j] > d[j+1]: d[j], d[j+1] = d[j+1], d[j]
        return d

class Sorter:
    def __init__(self, strategy: SortStrategy):
        self.strategy = strategy
    def run(self, data):
        return self.strategy.sort(data)

Dependency Injection

@Service
class OrderService {
    private final OrderRepo repo;
    private final PaymentGateway gateway;
    public OrderService(OrderRepo r, PaymentGateway g) {  // constructor inject
        this.repo = r; this.gateway = g;
    }
}

Immutable Value Object (Java record)

public record Money(long cents, String currency) {
    public Money {
        if (cents < 0) throw new IllegalArgumentException();
    }
    public Money add(Money other) {
        if (!currency.equals(other.currency)) throw new IllegalArgumentException();
        return new Money(cents + other.cents, currency);
    }
}

Sealed Hierarchy (Java 17+, Kotlin, Scala)

public sealed interface Shape permits Circle, Square, Triangle {}
public record Circle(double r) implements Shape {}
public record Square(double s) implements Shape {}
public record Triangle(double a, double b, double c) implements Shape {}

double area(Shape s) {
    return switch (s) {  // exhaustive
        case Circle c -> Math.PI * c.r() * c.r();
        case Square q -> q.s() * q.s();
        case Triangle t -> { /* heron */ yield 0; }
    };
}

매 결정 기준

상황	Approach
매 stateful entity (User, Order)	OOP class + invariant
매 stateless transformation	functional / pure function
매 plugin / extensibility	interface + DI
매 data-only	record / dataclass
매 algorithm dispatch	strategy / sealed + switch

기본값: 매 immutable record + composition + interface + constructor DI. 매 deep inheritance 의 X.

🔗 Graph

• 변형: Functional Programming
• 응용: Design Patterns · SOLID
• Adjacent: Domain-Driven Design · TypeScript 타입 시스템 (TypeScript Type System) · Encapsulation

🤖 LLM 활용

언제: class design review, SOLID 위반 발견, refactor toward composition. 언제 X: 매 simple data transformation script — function 으로 충분.

❌ 안티패턴

• God Object: 1000+ method 의 single class.
• Yo-yo Inheritance: 매 6 단 deep — 매 행위 추적 불가.
• Anemic Object: getter/setter 만, behavior 누락.
• Setter explosion: 매 invariant 의 무력화.
• Tight coupling to concrete class: 매 testability X.

🧪 검증 / 중복

• Verified (Gamma et al. GoF Design Patterns 1994, Martin Clean Architecture 2017).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — 4 기둥 + composition + sealed hierarchy + DI