컴퍼지트 패턴: 부분이 변화하더라도 기존 코드를 변경시키지 않도록 하는 패턴

기존 코드: 컴퓨터 클래스는 키보드, 본체, 모니터 클래스와 Composition 관계이다.

class Keyboard{
	private int price;
	private int power;
	public Keyboard(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Body{
	private int price;
	private int power;
	public Body(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Monitor{
	private int price;
	private int power;
	public Monitor(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Computer{
	private Body body;
	private Keyboard keyboard;
	private Monitor monitor;
	
	public void addBody(Body body) {
		this.body=body;
	}
	public void addKeyboard(Keyboard keyboard) {
		this.keyboard=keyboard;
	}
	public void addMonitor(Monitor monitor) {
		this.monitor=monitor;
	}
	public int getPrice() {
		int bodyPrice=body.getPrice();
		int keyboardPrice=keyboard.getPrice();
		int monitorPrice=monitor.getPrice();
		return bodyPrice+keyboardPrice+monitorPrice;
	}
	public int getPower() {
		int bodyPower=body.getPower();
		int keyboardPower=keyboard.getPower();
		int monitorPower=monitor.getPower();
		return bodyPower+keyboardPower+monitorPower;
	}
}

public class Client{
	public static void main(String[] args) {
		Body body=new Body(100,70);
		Keyboard keyboard=new Keyboard(5,2);
		Monitor monitor=new Monitor(20,30);
		
		// Computer 객체를 생성하고 부품 객체들을 설정함
		Computer computer=new Computer();
		computer.addBody(body);
		computer.addKeyboard(keyboard);
		computer.addMonitor(monitor);
		
		// 컴퓨터의 가격과 전력소비량을 구함
		int computerPrice=computer.getPrice();
		int computerPower=computer.getPower();
		System.out.println("Computer Power: "+computerPower+" W");
		System.out.println("Computer Price: "+computerPrice+" 만원");
	}
}

문제점: 만약 부품으로 스피커나 마우스가 추가되면 기존의 Computer 클래스를 수정해야 된다. -> OCP 위배

해결 방법: 구체적인 부품들을 일반화한 클래스를 정의하고 이를 가리키도록 설계한다.

abstract class ComputerDevice{
	public abstract int getPrice();
	public abstract int getPower();
}

class Keyboard extends ComputerDevice{
	private int price;
	private int power;
	public Keyboard(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Body extends ComputerDevice{
	private int price;
	private int power;
	public Body(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Monitor extends ComputerDevice{
	private int price;
	private int power;
	public Monitor(int power, int price) {
		this.power=power;
		this.price=price;
	}
	public int getPrice() {
		return price;
	}
	public int getPower() {
		return power;
	}
}

class Computer extends ComputerDevice{
	// 복수 개의 ComputerDevice를 가리킴
	private List<ComputerDevice> components=new ArrayList<ComputerDevice>();
	// ComputerDevice를 Computer에 추가
	public void addComponent(ComputerDevice component) {
		components.add(component);
	}
	// ComputerDevice를 Computer에서 제거
	public void removeComponent(ComputerDevice component) {
		components.remove(component);
	}
	
	public int getPrice() {
		int price=0;
		for(ComputerDevice component:components)
			price+=component.getPrice();
		return price;
	}
	
	public int getPower() {
		int power=0;
		for(ComputerDevice component:components)
			power+=component.getPower();
		return power;
	}
}

public class Client{
	public static void main(String[] args) {
		Body body=new Body(100,70);
		Keyboard keyboard=new Keyboard(5,2);
		Monitor monitor=new Monitor(20,30);
		
		// Computer 객체를 생성하고 부품 객체들을 설정함
		Computer computer=new Computer();
		computer.addComponent(body);
		computer.addComponent(keyboard);
		computer.addComponent(monitor);
		
		// 컴퓨터의 가격과 전력소비량을 구함
		int computerPrice=computer.getPrice();
		int computerPower=computer.getPower();
		System.out.println("Computer Power: "+computerPower+" W");
		System.out.println("Computer Price: "+computerPrice+" 만원");
	}
}