역할과 구현의 분리

interface Notifier {
    void send(String message);
}

class ConsoleNotifier implements Notifier {
    public void send(String message) {
        System.out.println(message);
    }
}

Notifier notifier = new ConsoleNotifier();
notifier.send("게시글 공개");

public final class ConcreteNotifierDependency {
    public static void main(String[] args) {
        BoardService service = new BoardService(new SilentNotifier());
        service.publish("가입 인사");
    }

    private static final class BoardService {
        private final ConsoleNotifier notifier;

        BoardService(ConsoleNotifier notifier) {
            this.notifier = notifier;
        }

        void publish(String title) {
            notifier.notify(title);
        }
    }

    private static final class ConsoleNotifier {
        void notify(String title) {
            System.out.println("console=" + title);
        }
    }

    private static final class SilentNotifier {
        void notify(String title) {
            System.out.println("silent");
        }
    }
}

error: incompatible types: SilentNotifier cannot be converted to ConsoleNotifier

interface PostNotifier {
    void notify(String title);
}

public final class RoleBasedNotification {
    public static void main(String[] args) {
        BoardService console = new BoardService(new ConsoleNotifier());
        BoardService silent = new BoardService(new SilentNotifier());

        console.publish("가입 인사");
        silent.publish("로그인 구현");
    }

    private interface PostNotifier {
        void notifyPublished(String title);
    }

    private static final class BoardService {
        private final PostNotifier notifier;

        BoardService(PostNotifier notifier) {
            this.notifier = notifier;
        }

        void publish(String title) {
            System.out.println("published=" + title);
            notifier.notifyPublished(title);
        }
    }

    private static final class ConsoleNotifier implements PostNotifier {
        @Override public void notifyPublished(String title) {
            System.out.println("console=" + title);
        }
    }

    private static final class SilentNotifier implements PostNotifier {
        @Override public void notifyPublished(String title) {
            System.out.println("silent");
        }
    }
}

published=가입 인사
console=가입 인사
published=로그인 구현
silent

클라이언트 → 역할 계약 ← 구현 A / 구현 B / 구현 C

public final class BoardApplicationComposition {
    public static void main(String[] args) {
        Board board = new Board(2);
        PostNotifier notifier = new ConsoleNotifier();
        BoardApplication app = new BoardApplication(board, notifier);

        app.publish("가입 인사", 40);
        app.publish("로그인 구현", 50);
        System.out.println(board.summary());
    }

    private static final class BoardApplication {
        private final Board board;
        private final PostNotifier notifier;

        BoardApplication(Board board, PostNotifier notifier) {
            this.board = board;
            this.notifier = notifier;
        }

        void publish(String title, int viewCount) {
            if (board.add(title, viewCount)) notifier.notifyPublished(title);
        }
    }

    private interface PostNotifier { void notifyPublished(String title); }

    private static final class ConsoleNotifier implements PostNotifier {
        @Override public void notifyPublished(String title) {
            System.out.println("published=" + title);
        }
    }

    private static final class Board {
        private final Post[] entries;
        private int size;
        Board(int capacity) { entries = new Post[capacity]; }
        boolean add(String title, int viewCount) {
            if (size == entries.length || title.isBlank() || viewCount <= 0) return false;
            entries[size++] = new Post(title, viewCount);
            return true;
        }
        String summary() {
            int total = 0;
            for (int index = 0; index < size; index++) {
                total += entries[index].viewCount();
            }
            return "count=" + size + ", total=" + total;
        }
    }

    private record Post(String title, int viewCount) {}
}

published=가입 인사
published=로그인 구현
count=2, total=90