인터페이스 다중 구현

public final class MultipleClassInheritance {
    private static class Timed {}
    private static class Named {}

    private static final class Post extends Timed, Named {}
}

error: '{' expected

final class CodePost extends Post implements Moderatable, Exportable {
}

public final class MultipleInterfaceRoles {
    public static void main(String[] args) {
        CodePost codePost = new CodePost("로그인 구현", 50);

        publish(codePost);
        moderate(codePost);
        export(codePost);
    }

    private static void publish(Publishable post) {
        post.publish();
    }

    private static void moderate(Moderatable value) {
        System.out.println("priority=" + value.priority());
    }

    private static void export(Exportable value) {
        System.out.println(value.exportText());
    }

    private interface Publishable { void publish(); }
    private interface Moderatable { int priority(); }
    private interface Exportable { String exportText(); }

    private static final class CodePost implements Publishable, Moderatable, Exportable {
        private final String title;
        private final int viewCount;

        CodePost(String title, int viewCount) {
            this.title = title;
            this.viewCount = viewCount;
        }

        @Override public void publish() { System.out.println("publish=" + title); }
        @Override public int priority() { return 100; }
        @Override public String exportText() { return title + "," + viewCount; }
    }
}

publish=로그인 구현
priority=100
로그인 구현,50

public final class ClassAndInterfaces {
    public static void main(String[] args) {
        CodePost post = new CodePost("로그인 구현", 50, "feature/login");

        Post base = post;
        Moderatable moderated = post;
        Exportable exported = post;

        base.publish();
        System.out.println("priority=" + moderated.priority());
        System.out.println("export=" + exported.exportText());
    }

    private interface Moderatable { int priority(); }
    private interface Exportable { String exportText(); }

    private abstract static class Post {
        private final String title;
        private final int viewCount;

        Post(String title, int viewCount) {
            this.title = title;
            this.viewCount = viewCount;
        }

        protected String title() { return title; }
        protected int viewCount() { return viewCount; }
        abstract void publish();
    }

    private static final class CodePost extends Post implements Moderatable, Exportable {
        private final String branch;

        CodePost(String title, int viewCount, String branch) {
            super(title, viewCount);
            this.branch = branch;
        }

        @Override void publish() { System.out.println("code=" + branch); }
        @Override public int priority() { return 100; }
        @Override public String exportText() { return title() + ":" + viewCount(); }
    }
}

code=feature/login
priority=100
export=로그인 구현:50

public final class DefaultRoleChoice {
    public static void main(String[] args) {
        System.out.println(new CodePost().label());
    }

    private interface Exportable {
        default String label() { return "export"; }
    }

    private interface Previewable {
        default String label() { return "preview"; }
    }

    private static final class CodePost implements Exportable, Previewable {
        @Override public String label() {
            return Exportable.super.label() + "+" + Previewable.super.label();
        }
    }
}

export+preview

public final class RoleBasedBoard {
    public static void main(String[] args) {
        Board board = new Board(3);
        board.add(new TextPost("가입 인사", 40));
        board.add(new CodePost("로그인 구현", 50));

        board.publishAll();
        board.exportAll();
        System.out.println(board.summary());
    }

    private static final class Board {
        private final Post[] posts;
        private int size;

        Board(int capacity) { posts = new Post[capacity]; }

        void add(Post post) {
            if (size == posts.length) throw new IllegalStateException("full");
            posts[size++] = post;
        }

        void publishAll() {
            for (int index = 0; index < size; index++) {
                posts[index].publish();
            }
        }

        void exportAll() {
            for (int index = 0; index < size; index++) {
                Post post = posts[index];
                if (post instanceof Exportable exported) {
                    System.out.println("export=" + exported.exportText());
                }
            }
        }

        String summary() {
            int total = 0;
            for (int index = 0; index < size; index++) {
                total += posts[index].viewCount();
            }
            return "count=" + size + ", total=" + total;
        }
    }

    private interface Exportable { String exportText(); }

    private abstract static class Post {
        private final String title;
        private final int viewCount;
        Post(String title, int viewCount) { this.title = title; this.viewCount = viewCount; }
        String title() { return title; }
        int viewCount() { return viewCount; }
        abstract void publish();
    }

    private static final class TextPost extends Post {
        TextPost(String title, int viewCount) { super(title, viewCount); }
        @Override void publish() { System.out.println("publish=text:" + title()); }
    }

    private static final class CodePost extends Post implements Exportable {
        CodePost(String title, int viewCount) { super(title, viewCount); }
        @Override void publish() { System.out.println("publish=code:" + title()); }
        @Override public String exportText() { return title() + "," + viewCount(); }
    }
}

publish=text:가입 인사
publish=code:로그인 구현
export=로그인 구현,50
count=2, total=90