Social media

Interfaces
java
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// User Interface
public interface IUser {
    String getUsername();
    void setUsername(String username);
    void postMessage(String message);
    void follow(IUser user);
    void unfollow(IUser user);
}

// Post Interface
public interface IPost {
    String getContent();
    void setContent(String content);
    IUser getAuthor();
    void addComment(IComment comment);
    List<IComment> getComments();
}

// Comment Interface
public interface IComment {
    String getContent();
    void setContent(String content);
    IUser getAuthor();
}
Implementations
java
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import java.util.ArrayList;
import java.util.List;

// User Implementation
public class User implements IUser {
    private String username;
    private List<IUser> following;
    private List<IPost> posts;

    public User(String username) {
        this.username = username;
        this.following = new ArrayList<>();
        this.posts = new ArrayList<>();
    }

    @Override
    public String getUsername() {
        return username;
    }

    @Override
    public void setUsername(String username) {
        this.username = username;
    }

    @Override
    public void postMessage(String message) {
        IPost post = new Post(message, this);
        posts.add(post);
    }

    @Override
    public void follow(IUser user) {
        if (!following.contains(user)) {
            following.add(user);
        }
    }

    @Override
    public void unfollow(IUser user) {
        following.remove(user);
    }
}

// Post Implementation
public class Post implements IPost {
    private String content;
    private IUser author;
    private List<IComment> comments;

    public Post(String content, IUser author) {
        this.content = content;
        this.author = author;
        this.comments = new ArrayList<>();
    }

    @Override
    public String getContent() {
        return content;
    }

    @Override
    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public IUser getAuthor() {
        return author;
    }

    @Override
    public void addComment(IComment comment) {
        comments.add(comment);
    }

    @Override
    public List<IComment> getComments() {
        return comments;
    }
}

// Comment Implementation
public class Comment implements IComment {
    private String content;
    private IUser author;

    public Comment(String content, IUser author) {
        this.content = content;
        this.author = author;
    }

    @Override
    public String getContent() {
        return content;
    }

    @Override
    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public IUser getAuthor() {
        return author;
    }
}
Main Class
java
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public class Main {
    public static void main(String[] args) {
        IUser alice = new User("Alice");
        IUser bob = new User("Bob");

        alice.follow(bob);

        alice.postMessage("Hello, world!");
        IPost alicePost = ((User)alice).getPosts().get(0);
        
        IComment comment = new Comment("Nice post!", bob);
        alicePost.addComment(comment);

        System.out.println(alicePost.getContent() + " by " + alicePost.getAuthor().getUsername());
        for (IComment c : alicePost.getComments()) {
            System.out.println("Comment: " + c.getContent() + " by " + c.getAuthor().getUsername());
        }
    }
}