CSE 11 Summer Session I 2024 PA4 - Simple Reddit

Due date: Sunday, September 1 @ 11:59PM PDT

Provided Files

None

Goal

This assignment is an introduction to Classes and ArrayLists in Java. In this assignment, you will create two new classes from scratch with several instance variables and methods.

Overview

Simple Reddit [Gradescope, 100 points]

• Implementation [90 points]
• Testing [10 points]

Simple Reddit

Reddit is a popular social news aggregation, content rating, and discussion website. Users submit content to the site such as links, text posts, images, and videos, which are then voted up or down by other members.

In this programming assignment, we will create a simplified version of Reddit, where users can create, upvote, and downvote posts. In order to do so, we will create two files: Post.java and User.java to represent and to implement the functionalities of these objects.

Implementation [90 Points]

Post.java

On Reddit, you can either create a post in some community (subreddit), or comment on someone's existing post. In this write-up, we will refer to them as "original posts" and "comments" to avoid confusion with a generic Post object. In our program, both are considered to be a Post, with some differences in instance variable values to differentiate them. The Post instance variables and methods are described below.

Warning

Do NOT add additional imports other than java.util.ArrayList.

Instance Variables:

public class Post {
    // ...
    private String title;
    private String content;
    private Post replyTo;
    private User author;
    private int upvoteCount;
    private int downvoteCount;
    // ...
}

• String title - the title of a Reddit post. If this post is a comment, then title should be null. title should be non-null if this post is an original post.
• String content - the content of a Reddit post. If this post is a comment, content is the comment a User made.
• Post replyTo - the original post or comment this Post is replying to. If this Post is an original post, replyTo should be null. replyTo should be non-null if this post is a comment.
• User author - the author of this Post.
• int upvoteCount - the number of upvotes of this Post.
• int downvoteCount - the number of downvotes of this Post.

Methods:

public class Post {
    // ...
    public Post(String title, String content, User author);
    public Post(String content, Post replyTo, User author);
    public String getTitle();
    public Post getReplyTo();
    public User getAuthor();
    public int getUpvoteCount();
    public int getDownvoteCount();
    public void updateUpvoteCount(boolean isIncrement);
    public void updateDownvoteCount(boolean isIncrement);
    public ArrayList<Post> getThread();
    public String toString();
    // ...
}

public Post(String title, String content, User author)

• The constructor for initializing an original post.
• Initialize the instance variables with the values from parameters.
• Set upvoteCount to 1. (The author upvotes their own post by default.) Set downvoteCount to 0.
• In the constructor, you will only need to initialize the class instance variables.
• You may also assume that after creating a Post, a separate and correct call to addPost will be used to add the post to the User.

public Post(String content, Post replyTo, User author)

• The constructor for initializing a comment.
• Initialize the instance variables with the values from parameters.
• Set upvoteCount to 1. Set downvoteCount to 0.

public String getTitle()

• Return the title of this Post.

public Post getReplyTo()

• Return the Post of that this Post is replying to.

public User getAuthor()

• Return the author of this Post.

public int getUpvoteCount()

• Return the number of upvotes of this Post.

public int getDownvoteCount()

• Return the number of downvotes of this Post.

public void updateUpvoteCount(boolean isIncrement)

• Increment upvoteCount by 1 if isIncrement is true, otherwise decrement upvoteCount by 1.
• You may assume that we will not call updateUpvoteCount that would result in a negative upvoteCount.

public void updateDownvoteCount(boolean isIncrement)

• Increment downvoteCount by 1 if isIncrement is true, otherwise decrement downvoteCount by 1.
• You may assume that we will not call updateDownvoteCount that would result in a negative downvoteCount.

public ArrayList<Post> getThread()

• Return a list of posts in the current thread, starting with the original post of this post and ending with this post.
• The original post should be the first item in the list, followed by its comment, then its comment's comment, etc. The last item in the list should be this post.
  • For example, if Post P1 is an original post, P2 is a reply (comment) to P1, and P3 is a reply to P2. Then P3.getThread() should return [P1, P2, P3]. Even if P1 has more than one reply comment, calling P3.getThread() should still return [P1, P2, P3]. Likewise, P3.getThread() should return [P1, P2, P3] even if there are replies to P3 or if P2 has replies other than P3.
  • If Post P1 is an original post, then P1.getThread() should return [P1] since there are no higher-level threads.
• You can implement this method either recursively or iteratively.

public String toString()

• Return a String representation of this Post.
• If this Post is an original post, the toString() should have the following format (\t is a tab):

  [upvoteCount|downvoteCount]\t Title
  \t Content
  

  Example:

  [1|0]   Title of Original Post
          Content of original post
  

• If this Post is a comment, the toString() should have the following format (\t is a tab):

  [upvoteCount|downvoteCount]\t Content
  

  Example:

  [2|0]   Content of a comment / reply
  

• Feel free to use the following format Strings with String.format() in your code:

  String TO_STRING_POST_FORMAT = "[%d|%d]\t%s\n\t%s";
  String TO_STRING_COMMENT_FORMAT = "[%d|%d]\t%s";

User.java

A User object represents a user in our simplified Reddit program. The User instance variables and methods are described below.

Warning

Do NOT add additional imports other than java.util.ArrayList.

Instance Variables:

public class User {
    // ...
    private int karma;
    private String username;
    private ArrayList<Post> posts;
    private ArrayList<Post> upvoted;
    private ArrayList<Post> downvoted;
    // ...
}

• String username - this User's username
• int karma
  • On Reddit, karma is like a user's score or reputation.
  • In our program, karma is calculated as (the total number of upvotes) - (the total number of downvotes) a user has. This value can be negative.
• ArrayList<Post> posts
  • A list of posts this User has made, including original posts and comments.
• ArrayList<Post> upvoted
  • A list of other users' posts that this User upvoted.
• ArrayList<Post> downvoted
  • A list of other users' posts that this User downvoted.

Methods:

public class User {
    // ...
    public User(String username);
    public void addPost(Post post);
    public void updateKarma();
    public int getKarma();
    public void upvote(Post post);
    public void downvote(Post post);
    public Post getTopPost();
    public Post getTopComment();
    public ArrayList<Post> getPosts();
    public String toString();
    // ...
}

public User(String username)

• The constructor for a User.
• Initialize username to the parameter value and all ArrayLists to empty ArrayLists. Initialize karma to 0.

public void addPost(Post post)

• Add a Post to end of this User's posts.
• If post is null, do not add it to posts.
• Update this User's karma by calling updateKarma().
• You may assume that we will only call addPost on the User that has authored the post.
• You may also assume that after creating a Post, a separate and correct call to addPost will be used to add the post to the User.

public void updateKarma()

• Update this User's karma by going through the user's posts and summing up upvoteCount$-$downvoteCount for each post.

public int getKarma()

• Return the current value of karma.

public void upvote(Post post)

• If post is null, return immediately.
• If post has already been upvoted by the User or if the author of post is the current user, return immediately as well.
• If post was originally downvoted by the User, remove it from downvoted and update post's downvoteCount accordingly.
• Add post to upvoted, update post's upvoteCount accordingly.
• Please add post to the end of the appropriate ArrayList when adding a post.
• Update the author's karma value. Make sure to update the karma of the user that authored the post, not the user that upvoted/downvoted the post. If you are passing the downvote tests but not all the upvote tests, please make sure you have updated the user karma correctly after upvote.

public void downvote(Post post)

• Similar to upvote.
• If post is null, return immediately.
• If post has already been downvoted by the User or if the author of post is the current user, return immediately as well.
• If post was originally upvoted by the User, remove it from upvoted and update post's upvoteCount accordingly.
• Add post to downvoted, update post's downvoteCount accordingly.
• Please add post to the end of the appropriate ArrayList when adding a post.
• Update the author's karma value. Make sure to update the karma of the user that authored the post, not the user that upvoted/downvoted the post.

public Post getTopPost()

• Return the top original post determined by the greatest (upvoteCount$-$downvoteCount) value.
• If no such original post exists, return null.
• If there is a tie, return the first original post Post in the tie. First meaning the lowest-indexed Post in posts.

public Post getTopComment()

• Return the top comment determined by the greatest (upvoteCount$-$downvoteCount) value.
• If no such comment exists, return null.
• If there is a tie, return the first comment Post in the tie. First meaning the lowest-indexed Post in posts.

public ArrayList<Post> getPosts()

• Return the list of posts (original posts and comments) made by the User.

public String toString()

• Return a String representation of this User.
• Format: u/username Karma: #
• Example: u/CSE11Student Karma: 2
• Feel free to use the following format String: "u/%s Karma: %d"

Testing [10 Points]

For this programming assignment, you will also be graded on your demonstration of testing your code.

Create a file called Tester.java. In the main method, create instances of User and Post, call the methods you would like to test, and use print statements to verify your code's correctness. For example, the following code tests the constructors, toString(), addPost(), getTopPost(), and getTopComment():

public class Tester {
    public static void main(String[] args) {
        User u1 = new User("CSE11Student");
        Post p1 = new Post("Title", "Content", u1);
        Post c1 = new Post("Comment", p1, u1);
        System.out.println(u1);
        System.out.println(p1);
        System.out.println(c1);
        u1.addPost(p1);
        u1.addPost(c1);
        System.out.println(u1.getTopPost());
        System.out.println(u1.getTopComment());
    }
}

Running the tester produces the expected results:

$ javac Post.java User.java Tester.java
$ java Tester
u/CSE11Student Karma: 0
[1|0]   Title
        Content
[1|0]   Comment
[1|0]   Title
        Content
[1|0]   Comment

To receive full credit for this section, make sure your main method tests at least 75% of both methods and lines of your code. You will be able to see your code coverage under "Coverage" on the Gradescope autograder. You'll get partial credits if your coverage is between 55% and 75%. No points will be awarded if your coverage is below 55%.

Submission

Submit the following file(s) to Gradescope by Sunday, September 1 @ 11:59PM PDT.

• Post.java
• User.java
• Tester.java

Even if your code does not pass all the tests, you will still be able to submit your work to receive partial points for the tests that you passed. Make sure your code compiles in order to receive partial credit.

How your assignment will be evaluated

• Correctness [90 points] You will earn points based on the autograder tests that your code passes. If the autograder tests are not able to run (e.g., your code does not compile, or it does not match the specifications in this writeup), you may not earn any credit.
  • Public Tests [45 points] These are tests of which you can always see the results after submission.
  • Hidden Tests [45 points] These are tests not visible to you until grades are published after the deadline.
• Testing [10 points] You will earn full points if your main method tests more than 75% of the lines and methods of User and Post.
• The prototypes of the classes User and Post are correct, which means that there are no other methods besides the required methods above and helper methods, and there are no other fields besides the required fields above and constants. Remember that you may create any number of additional helper methods and constants (as fields), but helper methods must be private, and constants must be static final fields of primitive or String types. Incorrect prototypes will result in a 0.
• You are only allowed to call methods in the classes User and Post, and in library classes listed below. Calling methods in other library classes will result in a 0.
  • java.lang.Integer
  • java.lang.Object
  • java.lang.String
  • java.lang.StringBuilder
  • java.util.ArrayList
  • java.util.Iterator
  • java.util.ListIterator
• You are only allowed to access fields (i.e. class variables and instance variables) in the classes User and Post, and constants. Accessing fields in other library classes that are not constants will result in a 0.
• You may use any library methods and fields in Tester.java, except for some methods that may undermine security, such as file I/O, file descriptor I/O, shell command execution, network I/O, access modification, etc. Exceptions will be thrown in the coverage test if you call library methods related to these functions.