update stack overflow solution

solutions/java/src/stackoverflow/Answer.java

@@ -1,49 +1,72 @@
 package stackoverflow;
 
+import java.util.ArrayList;
+import java.util.Date;
 import java.util.List;
 
-public class Answer {
+public class Answer implements Votable, Commentable {
     private final int id;
-    private final String body;
+    private final String content;
     private final User author;
     private final Question question;
+    private boolean isAccepted;
+    private final Date creationDate;
     private final List<Comment> comments;
-    private int voteCount;
+    private final List<Vote> votes;
 
-    public Answer(int id, String body, User author, Question question, List<Comment> comments, int voteCount) {
-        this.id = id;
-        this.body = body;
+    public Answer(User author, Question question, String content) {
+        this.id = generateId();
         this.author = author;
         this.question = question;
-        this.comments = comments;
-        this.voteCount = voteCount;
+        this.content = content;
+        this.creationDate = new Date();
+        this.votes = new ArrayList<>();
+        this.comments = new ArrayList<>();
+        this.isAccepted = false;
     }
 
-    public void setVoteCount(int voteCount) {
-        this.voteCount = voteCount;
+    @Override
+    public void vote(User user, int value) {
+        if (value != 1 && value != -1) {
+            throw new IllegalArgumentException("Vote value must be either 1 or -1");
+        }
+        votes.removeIf(v -> v.getUser().equals(user));
+        votes.add(new Vote(user, value));
+        author.updateReputation(value * 10);  // +10 for upvote, -10 for downvote
     }
 
-    public int getId() {
-        return id;
+    @Override
+    public int getVoteCount() {
+        return votes.stream().mapToInt(Vote::getValue).sum();
     }
 
-    public String getBody() {
-        return body;
+    @Override
+    public void addComment(Comment comment) {
+        comments.add(comment);
     }
 
-    public User getAuthor() {
-        return author;
+    @Override
+    public List<Comment> getComments() {
+        return new ArrayList<>(comments);
     }
 
-    public Question getQuestion() {
-        return question;
+    public void markAsAccepted() {
+        if (isAccepted) {
+            throw new IllegalStateException("This answer is already accepted");
+        }
+        isAccepted = true;
+        author.updateReputation(15);  // +15 reputation for accepted answer
     }
 
-    public List<Comment> getComments() {
-        return comments;
+    private int generateId() {
+        return (int) (System.currentTimeMillis() % Integer.MAX_VALUE);
     }
 
-    public int getVoteCount() {
-        return voteCount;
-    }
-}
+    // Getters
+    public int getId() { return id; }
+    public User getAuthor() { return author; }
+    public Question getQuestion() { return question; }
+    public String getContent() { return content; }
+    public Date getCreationDate() { return creationDate; }
+    public boolean isAccepted() { return isAccepted; }
+}

solutions/java/src/stackoverflow/Comment.java

@@ -1,10 +1,27 @@
 package stackoverflow;
 
-import java.security.Timestamp;
+import java.util.Date;
 
 public class Comment {
-    private int id;
-    private String text;
-    private User author;
-    private Timestamp createdAt;
-}
+    private final int id;
+    private final String content;
+    private final User author;
+    private final Date creationDate;
+
+    public Comment(User author, String content) {
+        this.id = generateId();
+        this.author = author;
+        this.content = content;
+        this.creationDate = new Date();
+    }
+
+    private int generateId() {
+        return (int) (System.currentTimeMillis() % Integer.MAX_VALUE);
+    }
+
+    // Getters
+    public int getId() { return id; }
+    public User getAuthor() { return author; }
+    public String getContent() { return content; }
+    public Date getCreationDate() { return creationDate; }
+}

solutions/java/src/stackoverflow/Commentable.java

@@ -0,0 +1,8 @@
+package stackoverflow;
+
+import java.util.List;
+
+public interface Commentable {
+    void addComment(Comment comment);
+    List<Comment> getComments();
+}

solutions/java/src/stackoverflow/Question.java

@@ -1,61 +1,76 @@
 package stackoverflow;
 
+import java.util.ArrayList;
+import java.util.Date;
 import java.util.List;
 
-public class Question {
+public class Question implements Votable, Commentable {
     private final int id;
     private final String title;
-    private final String body;
+    private final String content;
     private final User author;
+    private final Date creationDate;
     private final List<Answer> answers;
     private final List<Comment> comments;
     private final List<Tag> tags;
-    private int voteCount;
+    private final List<Vote> votes;
 
-    public Question(int id, String title, String body, User author, List<Answer> answers, List<Comment> comments, List<Tag> tags, int voteCount) {
-        this.id = id;
-        this.title = title;
-        this.body = body;
+    public Question(User author, String title, String content, List<String> tagNames) {
+        this.id = generateId();
         this.author = author;
-        this.answers = answers;
-        this.comments = comments;
-        this.tags = tags;
-        this.voteCount = voteCount;
-    }
-
-    public void setVoteCount(int voteCount) {
-        this.voteCount = voteCount;
-    }
-
-    public int getId() {
-        return id;
+        this.title = title;
+        this.content = content;
+        this.creationDate = new Date();
+        this.answers = new ArrayList<>();
+        this.tags = new ArrayList<>();
+        this.votes = new ArrayList<>();
+        this.comments = new ArrayList<>();
+        for (String tagName : tagNames) {
+            this.tags.add(new Tag(tagName));
+        }
     }
 
-    public String getTitle() {
-        return title;
+    public void addAnswer(Answer answer) {
+        if (!answers.contains(answer)) {
+            answers.add(answer);
+        }
     }
 
-    public String getBody() {
-        return body;
+    @Override
+    public void vote(User user, int value) {
+        if (value != 1 && value != -1) {
+            throw new IllegalArgumentException("Vote value must be either 1 or -1");
+        }
+        votes.removeIf(v -> v.getUser().equals(user));
+        votes.add(new Vote(user, value));
+        author.updateReputation(value * 5);  // +5 for upvote, -5 for downvote
     }
 
-    public User getAuthor() {
-        return author;
+    @Override
+    public int getVoteCount() {
+        return votes.stream().mapToInt(Vote::getValue).sum();
     }
 
-    public List<Answer> getAnswers() {
-        return answers;
+    @Override
+    public void addComment(Comment comment) {
+        comments.add(comment);
     }
 
+    @Override
     public List<Comment> getComments() {
-        return comments;
+        return new ArrayList<>(comments);
     }
 
-    public List<Tag> getTags() {
-        return tags;
+    private int generateId() {
+        return (int) (System.currentTimeMillis() % Integer.MAX_VALUE);
     }
 
-    public int getVoteCount() {
-        return voteCount;
-    }
-}
+    // Getters
+    public int getId() { return id; }
+    public User getAuthor() { return author; }
+    public String getTitle() { return title; }
+    public String getContent() { return content; }
+    public Date getCreationDate() { return creationDate; }
+    public List<Answer> getAnswers() { return new ArrayList<>(answers); }
+    public List<Tag> getTags() { return new ArrayList<>(tags); }
+}

solutions/java/src/stackoverflow/StackOverflow.java

@@ -1,100 +1,77 @@
 package stackoverflow;
 
-import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
 
 public class StackOverflow {
-    private static StackOverflow instance;
     private final Map<Integer, User> users;
     private final Map<Integer, Question> questions;
-    private final Map<String, List<Question>> taggedQuestions;
+    private final Map<Integer, Answer> answers;
+    private final Map<String, Tag> tags;
 
-    private StackOverflow() {
+    public StackOverflow() {
         users = new ConcurrentHashMap<>();
         questions = new ConcurrentHashMap<>();
-        taggedQuestions = new ConcurrentHashMap<>();
+        answers = new ConcurrentHashMap<>();
+        tags = new ConcurrentHashMap<>();
     }
 
-    public static synchronized StackOverflow getInstance() {
-        if (instance == null) {
-            instance = new StackOverflow();
-        }
-        return instance;
-    }
-
-    public void registerUser(User user) {
-        users.put(user.getId(), user);
+    public User createUser(String username, String email) {
+        int id = users.size() + 1;
+        User user = new User(id, username, email);
+        users.put(id, user);
+        return user;
     }
 
-    public User loginUser(String username, String password) {
-        for (User user : users.values()) {
-            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {
-                return user;
-            }
-        }
-        return null;
-    }
-
-    public void postQuestion(Question question) {
+    public Question askQuestion(User user, String title, String content, List<String> tags) {
+        Question question = user.askQuestion(title, content, tags);
         questions.put(question.getId(), question);
         for (Tag tag : question.getTags()) {
-            taggedQuestions.computeIfAbsent(tag.getName(), k -> new ArrayList<>()).add(question);
+            this.tags.putIfAbsent(tag.getName(), tag);
         }
+        return question;
     }
 
-    public void postAnswer(Answer answer) {
-        Question question = answer.getQuestion();
-        question.getAnswers().add(answer);
+    public Answer answerQuestion(User user, Question question, String content) {
+        Answer answer = user.answerQuestion(question, content);
+        answers.put(answer.getId(), answer);
+        return answer;
     }
 
-    public void postComment(Comment comment) {
-        // Add comment to the respective question or answer
-        // ...
+    public Comment addComment(User user, Commentable commentable, String content) {
+        return user.addComment(commentable, content);
     }
 
-    public void voteQuestion(Question question, int value) {
-        synchronized (question) {
-            question.setVoteCount(question.getVoteCount() + value);
-        }
-        updateUserReputation(question.getAuthor(), value);
+    public void voteQuestion(User user, Question question, int value) {
+        question.vote(user, value);
     }
 
-    public void voteAnswer(Answer answer, int value) {
-        synchronized (answer) {
-            answer.setVoteCount(answer.getVoteCount() + value);
-        }
-        updateUserReputation(answer.getAuthor(), value);
+    public void voteAnswer(User user, Answer answer, int value) {
+        answer.vote(user, value);
     }
 
-    private void updateUserReputation(User user, int value) {
-        synchronized (user) {
-            user.setReputation(user.getReputation() + value);
-        }
+    public void acceptAnswer(Answer answer) {
+        answer.markAsAccepted();
     }
 
     public List<Question> searchQuestions(String query) {
-        List<Question> results = new ArrayList<>();
-        for (Question question : questions.values()) {
-            if (question.getTitle().contains(query) || question.getBody().contains(query)) {
-                results.add(question);
-            }
-        }
-        return results;
-    }
-
-    public List<Question> getQuestionsByTag(String tagName) {
-        return taggedQuestions.getOrDefault(tagName, new ArrayList<>());
+        return questions.values().stream()
+                .filter(q -> q.getTitle().toLowerCase().contains(query.toLowerCase()) ||
+                        q.getContent().toLowerCase().contains(query.toLowerCase()) ||
+                        q.getTags().stream().anyMatch(t -> t.getName().equalsIgnoreCase(query)))
+                .collect(Collectors.toList());
     }
 
     public List<Question> getQuestionsByUser(User user) {
-        List<Question> results = new ArrayList<>();
-        for (Question question : questions.values()) {
-            if (question.getAuthor().equals(user)) {
-                results.add(question);
-            }
-        }
-        return results;
+        return user.getQuestions();
     }
-}
+
+    // Getters
+    public User getUser(int id) { return users.get(id); }
+    public Question getQuestion(int id) { return questions.get(id); }
+    public Answer getAnswer(int id) { return answers.get(id); }
+    public Tag getTag(String name) { return tags.get(name); }
+}