stackoverflow

StackOverflow System (LLD)

Problem Statement

Design and implement a simplified StackOverflow-like Q&A platform. The system should allow users to post questions and answers, vote on them, comment, tag questions, and track user reputation.

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Requirements

• User Management: Users can ask questions, answer, comment, and vote.
• Questions & Answers: Users can post questions and answers. Each question can have multiple answers, and one accepted answer.
• Voting: Users can upvote or downvote questions and answers. Reputation is updated accordingly.
• Comments: Users can comment on both questions and answers.
• Tags: Questions can be tagged for categorization.
• Reputation: Users gain or lose reputation based on votes and accepted answers.
• Accepted Answer: The question author can mark one answer as accepted.

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Core Entities

• User: Represents a user, tracks reputation and user details.
• Question: Represents a question, holds answers, comments, tags, votes, and accepted answer.
• Answer: Represents an answer to a question, holds comments, votes, and accepted status.
• Comment: Represents a comment on a question or answer.
• Tag: Represents a tag for categorizing questions.
• Vote: Represents a vote (upvote/downvote) by a user on a question or answer.
• VoteType: Enum for UPVOTE and DOWNVOTE.
• Votable (interface): For entities that can be voted on.
• Commentable (interface): For entities that can be commented on.

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Class Design

UML Class Diagram

1. User

• Fields: id, name, reputation, etc.
• Methods: updateReputation(int delta), getReputation(), etc.

2. Question

• Fields: id, title, content, author, creationDate, answers, comments, tags, votes, acceptedAnswer
• Methods: addAnswer(Answer), acceptAnswer(Answer), vote(User, VoteType), getVoteCount(), addComment(Comment), getComments(), etc.

3. Answer

• Fields: id, content, author, question, isAccepted, creationDate, comments, votes
• Methods: vote(User, VoteType), getVoteCount(), addComment(Comment), getComments(), markAsAccepted(), etc.

4. Comment

• Fields: id, content, author, creationDate

5. Tag

• Fields: name

6. Vote

• Fields: voter, type (VoteType)
• Methods: getVoter(), getType()

7. VoteType

• Enum: UPVOTE, DOWNVOTE

8. Votable (interface)

• Methods: vote(User, VoteType), getVoteCount()

9. Commentable (interface)

• Methods: addComment(Comment), getComments()

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Design Patterns Used

• Strategy Pattern: For voting and commenting behaviors via interfaces.
• Observer Pattern: (Conceptually) for reputation updates on votes and accepted answers.

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Example Usage

User alice = new User("Alice");
Question q = new Question(alice, "What is Java?", "Explain Java basics.", Arrays.asList("java", "basics"));
User bob = new User("Bob");
Answer a = new Answer(bob, q, "Java is a programming language.");
q.addAnswer(a);
q.vote(bob, VoteType.UPVOTE);
a.vote(alice, VoteType.UPVOTE);
q.acceptAnswer(a);

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Demo

See StackOverflowDemo.java for a sample usage of the StackOverflow system.

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Extending the Framework

• Add new features: Such as badges, user profiles, or advanced search.
• Add new vote types: Extend VoteType and update logic in vote() methods.
• Add moderation: Implement admin/moderator roles for content management.

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