16 Composition relationship

프로그래밍에서의 "Composite relationship"와 "상속(Inheritance)"은 객체 지향 프로그래밍(OOP)에서 객체 간의 관계를 설명하는 두 가지 다른 개념입니다. 

Composite relationship은 일반적으로 객체들 간의 "has-a" 관계를 나타내는 데 사용되며, 이는 한 객체가 다른 객체를 포함하거나 그 일부로서 존재함을 의미합니다. 반면에 상속은 "is-a" 관계를 나타내며, 객체 간의 일반화와 특수화를 나타냅니다.

A는 B다 (A is B) → Inheritance (10%)
A는 B를 가지고 있다 (A has B) → Composition (90%)

 

// 부분 객체
class Engine {
    void start() {
        System.out.println("Engine starting");
    }
}

// 전체 객체
class Car {
    private Engine engine;

    Car() {
        // Composite relationship: Car has-a Engine
        this.engine = new Engine();
    }

    void start() {
        System.out.println("Car starting");
        engine.start(); // Car는 Engine을 포함하고 있음
    }
}

 

여기서 Car 클래스는 Engine 클래스를 포함하고 있습니다. Car는 Engine을 가지고 있으므로 Composite relationship이 성립합니다.

 

 

상속과 Composite relationship은 각각 다른 목적을 가지고 있으며, 어떤 상황에서 어떤 것을 사용할지는 설계의 의도와 특정한 요구사항에 따라 결정됩니다. 상속은 코드를 재사용하고 클래스 간에 일반화와 특수화를 통해 계층을 형성하는 데 사용되고, Composite relationship은 한 클래스가 다른 클래스를 포함하여 복합적인 객체를 구성하는 데 사용됩니다.

 

 

 

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A composite relationship refers to a connection between two objects or entities where one is considered a part or component of the other. It implies a "whole-part" association, often involving shared lifecycles between the objects.

Inheritance (IS-A) : IS-A relationship signifies that one object is a type of another. It is implemented using ‘extends’ and ‘implements’ keywords.

Composition : HAS-A relationship signifies that a class has a relationship with another class. For instance, Class A holds Class B’s reference and can access all properties of class B.