기본 _ Ch. 2

1. 회원 도메인

• 회원 가입 및 조회 가능
• 회원은 일반과 VIP로 구성
• DB는 미정

• 회원 저장소 인터페이스

public interface MemberRepository {
      void save(Member member);
      Member findById(Long memberId);
}

• 메모리 회원 저장소 구현체

public class MemoryMemberRepository implements MemberRepository{

    private static Map<Long, Member> store = new HashMap<>();

    @Override
    public void save(Member member) {store.put(member.getId(), member);}

    @Override
    public Member findById(Long memberId) {return store.get(memberId);}
}

• 문제점 : OCP 위반 ({new MemoryMemberRepository();} --> 구현체에 의존)

public class MemberServiceImpl implements MemberService{

    private final MemberRepository memberRepository = new MemoryMemberRepository(); //인터페이스가 아닌 구현체에 의존

    @Override
    public void join(Member member) {memberRepository.save(member);}

    @Override
    public Member findMember(Long memberId) {return memberRepository.findById(memberId);}
}

---

2. 주문과 할인 도메인

• 회원은 상품을 주문
• 회원 등급에 따른 할인
• 할인 정책은 미정
  

• 할인 정책 인터페이스

public interface DiscountPolicy {
    /**
     * @return 할인 대상 금액
     */
    int discount(Member member, int price);
}

• 할인 정책 구현체(정액)

public class FixDiscountPolicy implements DiscountPolicy {
    private int discountFixAmount = 1000;

    @Override
    public int discount(Member member, int price) {
        if (member.getGrade() == Grade.VIP) {
            return discountFixAmount;
        } else {return 0;}
    }
}

• 주문 서비스 인터페이스

public interface OrderService {
    Order createOrder(Long memberId, String itemName, int itemPrice);

}

• 주문 서비스 구현체

public class OrderServiceImpl implements OrderService{
    private final MemberRepository memberRepository = new MemoryMemberRepository();
    private final DiscountPolicy discountPolicy = new FixDiscountPolicy();

    @Override
    public Order createOrder(Long memberId, String itemName, int itemPrice) {
        Member member = memberRepository.findById(memberId);
        int discountPrice = discountPolicy.discount(member, itemPrice);

        return new Order(memberId, itemName, itemPrice, discountPrice);
    }
}