Building a Q&A Platform in Java: A Comprehensive Low level Design for StackOverflow-like Functionality

Designing a low-level system involves breaking down the high-level components into classes, methods, and interactions. Here’s a simplified Java implementation for a few critical components. This is just a starting point, and you may need to expand and refine it based on specific requirements.

User Class

public class User {
    private int userID;
    private String username;
    private String password;
    private String email;
    private int reputation;

    // Constructors, getters, and setters

    public boolean authenticate(String enteredPassword) {
        return this.password.equals(enteredPassword);
    }
}

Question Class:

import java.util.ArrayList;
import java.util.List;

public class Question {
    private int questionID;
    private String title;
    private String content;
    private User author;
    private long timestamp;
    private int upvotes;
    private int downvotes;
    private int reports;
    private boolean hidden;
    private List<Reply> replies;

    // Constructors, getters, and setters

    public void addReply(Reply reply) {
        replies.add(reply);
    }

    public void upvote() {
        upvotes++;
    }

    public void downvote() {
        downvotes++;
    }

    public void report() {
        reports++;
    }

    public void hide() {
        hidden = true;
    }
}

Reply class:

import java.util.ArrayList;
import java.util.List;

public class Reply implements Post {
    private int replyID;
    private Question parentQuestion;
    private String content;
    private User author;
    private long timestamp;
    private int upvotes;
    private int downvotes;
    private int reports;
    private boolean hidden;
    private List<Reply> nestedReplies;

    // Constructors, getters, and setters

    public void addNestedReply(Reply nestedReply) {
        nestedReplies.add(nestedReply);
    }

    // Implement Post interface methods

    @Override
    public int getID() {
        return replyID;
    }

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

    @Override
    public long getTimestamp() {
        return timestamp;
    }

    @Override
    public int getUpvotes() {
        return upvotes;
    }

    @Override
    public int getDownvotes() {
        return downvotes;
    }

    @Override
    public int getReports() {
        return reports;
    }

    @Override
    public boolean isHidden() {
        return hidden;
    }

    @Override
    public void upvote() {
        upvotes++;
    }

    @Override
    public void downvote() {
        downvotes++;
    }

    @Override
    public void report() {
        reports++;
    }

    @Override
    public void hide() {
        hidden = true;
    }
}

Category class:

public class Category {
    private int categoryID;
    private String name;
    private String description;

    // Constructors, getters, and setters
}

Admin class :

public class Admin extends User {

    // Admin-specific methods for managing users, questions, and replies
    public void hidePost(Post post) {
        post.hide();
    }

    public void handleSpam(User user) {
        // Implement spam-handling logic
    }
}

PostManager class:

import java.util.List;

public class PostManager {
    private List<Post> posts;

    public PostManager(List<Post> posts) {
        this.posts = posts;
    }

    public void addQuestion(Question question) {
        posts.add(question);
    }

    public void deletePost(Post post) {
        posts.remove(post);
    }

    public void upvote(Post post) {
        post.upvote();

        // Optionally, you might want to update the list if necessary
        // posts.set(posts.indexOf(post), post);
    }

    public void downvote(Post post) {
        post.downvote();
    }

    public void report(Post post) {
        post.report();
    }

    public void handleSpam(User user) {
        // Placeholder logic to handle spam
        System.out.println("Handling spam for user: " + user.getUsername());
    }

    // Other methods...

    public List<Post> getPosts() {
        return posts;
    }
}

Usage:

public class UsageExample {
    public static void main(String[] args) {
        // Create a PostManager
        PostManager postManager = new PostManager();

        // Add a new question
        Question question1 = new Question(/* question details */);
        postManager.addQuestion(question1);

        // Upvote the first question
        PostManager.upvote(question1);

        // Add another question
        Question question2 = new Question(/* question details */);
        postManager.addQuestion(question2);

        // Downvote the second question
        PostManager.downvote(question2);

        // Report the second question
        PostManager.report(question2);

        // Print all posts
        System.out.println("All Posts:");
        List<Post> allPosts = postManager.getPosts();
        for (Post post : allPosts) {
            System.out.println("Post ID: " + post.getID() +
                    ", Author: " + post.getAuthor().getUsername() +
                    ", Upvotes: " + post.getUpvotes() +
                    ", Downvotes: " + post.getDownvotes() +
                    ", Reports: " + post.getReports());
        }

        // Handle spam (this could be part of an Admin functionality)
        PostManager.handleSpam(question2.getAuthor());

        // Print posts after handling spam
        System.out.println("\nPosts after handling spam:");
        List<Post> remainingPosts = postManager.getPosts();
        for (Post post : remainingPosts) {
            System.out.println("Post ID: " + post.getID() +
                    ", Author: " + post.getAuthor().getUsername() +
                    ", Upvotes: " + post.getUpvotes() +
                    ", Downvotes: " + post.getDownvotes() +
                    ", Reports: " + post.getReports());
        }
    }
}