CSE 8B: Introduction to Programming II
Programming Assignment 5
Objects and Classes
Due: Monday, February 24, 11:59 PM
Learning goals:
● Implement a simplified Reddit program using Java classes
● Use the Java ArrayList class
● Write unit tests for your classes
This assignment must be completed INDIVIDUALLY.
Coding Style [10 points]
For this programming assignment, we will be enforcing the CSE 8B and 11 Coding Style Guidelines. These guidelines can also be found on Canvas and the class website. Please ensure to have complete file headers, class headers and method headers. Avoid using magic numbers, use consistent indentation and keep your lines short.
Getting the Starter Code
1. You can download the starter code from Piazza → Resources → Homework → PA5.zip
2. After compiling Post.java and User.java, you should see the following in your terminal
$ javac Post.java
Post.java:65: error: cannot find symbol
P1.upvoteCount = 5;
^
symbol: variable upvoteCount
location: variable P1 of type Post
...
$ javac User.java
User.java:55: error: cannot find symbol
U1.karma = 10;
^
symbol: variable karma
location: variable U1 of type User
...
These compiler errors are expected, as the method unitTests is trying to reference things that have not yet been implemented in the starter code! Things should compile cleanly once you've added in the instance variables for each class.
You MUST NOT include any package statements in your code.
Overview
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. To do so, you will be completing the implementation of two classes: Post.java and User.java
Part 1: Implementation [80 points]
Post.java
On Reddit, a post can exist as a stand-alone post in some community (subreddit) or as a comment on someone else's stand-alone post. In this write-up, we shall refer to the first type of post as an "original post" and the second type of post as a "comment". Both types of posts will be represented by the Post class (we'll use Post's instance variables to help us indicate whether a particular Post object is representing an original post or a comment)
In this part of the assignment, you will implement the Post class which represents the properties of a reddit post. The UML diagram for the Post class is:
To summarize, the Post class contains the following fields:
private String title
● The title of this Post. If this Post represents a comment, then title must be null. If this Post represents an original post, then title should be non-null.
private String content
● The content of this reddit Post.
private Post replyTo
● The Post object that this Post is replying to. If this Post is an original post, replyTo must be null. If this Post is a comment, then replyTo must be non-null.
private User author
● The author (represented as a User object) of this Post.
private int upvoteCount
● The number of upvotes that this Post has.
private int downvoteCount
● The number of downvotes that this Post has. and the following methods:
public Post(String title, String content, User author)
● The constructor for initializing an original post.
● This constructor must set the title, content, and author fields of this Post object with the values from the parameters (e.g., the title field must be assigned the contents of the title parameter).
● Set upvoteCount and downvoteCount to 0.
● Set replyTo to null.
public Post(String content, Post replyTo, User author)
● The constructor for initializing a comment.
● This constructor must set the content, replyTo, and author fields of this Post object with the values from the parameters (e.g., the content field must be assigned the contents of the content parameter).
● Set upvoteCount and downvoteCount to 0.
● Set title to null.
public String getTitle()
● Return the title of this Post.
public Post get ReplyTo()
● Return the Post object that this Post is replying to.
public User getAuthor()
● Return the author of this Post.
public int getUpvoteCount()
● Return the number of upvotes that this Post has.
public int getDownvoteCount()
● Return the number of downvotes that this Post has.
public void updateUpvoteCount(boolean is Increment)
● Increment the upvoteCount of this Post by 1 if is Increment is true. Otherwise, decrement upvoteCount by 1.
● You may assume that we will not call updateUpvoteCount in such a way that would result in a negative upvoteCount value in any of our tests.
public void updateDownvoteCount(boolean is Increment)
● Increment the downvoteCount of this Post by 1 if is Increment is true. Otherwise, decrement downvoteCount by 1.
● You may assume that we will not call updateDownvoteCount in such a way that would result in a negative downvoteCount value in any of our tests.
public ArrayList<Post> getThread()
● Return an ArrayList of Posts in the current thread, starting with the original post and ending with this Post.
● The original post should be the first item in the ArrayList, followed by one of its comments, followed by another one of its comments, and so on until this Post is reached.
● For example, suppose that P1 is an original post, P2 is a comment on P1, and P3 is a comment on P2. Then P3.getThread() must return [P1, P2, P3]. In other words, the "current thread" is the collection of posts that originate from this Post and "climbs up" through the replyTo fields to reach the original post.
○ If P1 were to have more than one comment, P3.getThread() must still return [P1, P2, P3].
● You may implement this method iteratively or recursively.
public String toString()
● Return a String representation of this Post.
● If this Post is an original post, its String representation must follow the format
[<upvoteCount>|<downvoteCount>]\t<title>\n
\t<content>
● Original Post Example
[1 |0] Title of Original Post
Content of original post
● If this Post is a comment, the String representation must follow the format
[<upvoteCount>|<downvoteCount>]\t<content>
● Comment Example
[2 |0] Content of comment
● Implementation Notes
○ \t is a tab character.
○ You should not include angle brackets (i.e., <>) in the String you return.
○ In the above String formats, <field> should be populated with the
corresponding field value of this Post (without the angle brackets). We strongly recommend that you use the provided format string templates (along with the String.format() method) in your implementation of this method.
User.java
In this part of the assignment, you will implement the User class which represents the properties of a reddit user. The UML diagram for the User class is
To summarize, the User class contains the following fields:
private String username
● The username of this User.
private int karma
● The karma score of this User.
private ArrayList<Post> posts
● A list of Posts this User has authored, including original posts and comments.
private ArrayList<Post> upvoted
● A list of other User's Posts that this User has upvoted.
private ArrayList<Post> downvoted
● A list of other User's Posts that this User has downvoted. and the following methods:
public User(String username)
● The constructor for initializing a User.
● This constructor must set the username field of this Post object with the contents of the username parameter.
● Set karma to 0.
● Initialize posts, upvoted, and downvoted to empty ArrayLists using the no-argument ArrayList constructor.
public void addPost(Post post)
● Add post to the end of this User's lists of authored posts.
● If post is null, you must not add it to posts.
● Update this User's karma by calling updateKarma(). You must do this regardless of the value of post. If post is non-null, you must call updateKarma() after adding post to posts.
● You may assume that we will only call addPost on the User that has authored post.
public void updateKarma()
● Update this User's karma score by going through this User's authored posts and summing upvoteCount–downvoteCount for each post. In other words, after calling updateKarma() this User's karma must be equal to
where N is the number of posts this user has authored.
public int get Karma()
● Return this User's karma score.
public void upvote(Post post)
● If post is null, this method must do nothing and immediately return.
● If post has already been upvoted by this User OR if the author of post is this User, this method must do nothing and immediately return.
● If post already exists in this User's list of downvoted posts (downvoted), remove it from downvoted and update the downvoteCount of post accordingly.
● Add post to the end of this User's list of upvoted posts (upvoted) and update post's upvoteCount accordingly.
● Update the karma score of post's author by calling updateKarma() accordingly. You must do this if this method does not immediately return.
public void downvote(Post post)
● If post is null, this method must do nothing and immediately return.
● If post has already been downvoted by this User OR if the author of post is this User, this method must do nothing and immediately return.
● If post already exists in this User's list of upvoted posts (upvoted), remove it from upvoted and update the upvoteCount of post accordingly.
● Add post to the end of this User's list of downvoted posts (downvoted) and update post's downvoteCount accordingly.
● Update the karma score of post's author by calling updateKarma() accordingly. You must do this if this method does not immediately return.
public Post getTopOriginal Post()
● Return this User's top original post. That is, the original post authored by this User with the greatest upvoteCount–downvoteCount value.
● If this User does not have any original posts, return null.
● If the greatest upvoteCount–downvoteCount value is shared by multiple original posts, return the first original post in posts with this value.
public Post getTopComment()
● Return this User's top comment. This is, the comment authored by this User with the greatest upvoteCount–downvoteCount value.
● If this User does not have any comments, return null.
● If the greatest upvoteCount–downvoteCount value is shared by multiple comments, return the first comment in posts with this value.
public ArrayList<Post> get Posts()
● Return the list of posts authored by this User.
public String toString()
● Return the String representation of this User. The String representation of this User must follow the format
u/<username> Karma: <karma>
● Example
u/Widogast Karma: 9
● Implementation Notes
○ You should not include angle brackets (i.e., <>) in the String you return.
○ In the above String formats, <field> should be populated with the
corresponding field value of this User (without the angle brackets). We strongly recommend that you use the provided format string templates (along with the String.format() method) in your implementation of this method.
Part 2: Unit Testing [10 points]
In this part of the assignment, you will need to implement your own test cases in the method unitTests in both Post.java and User.java. Each file has its own unitTests method that you must fill out. To get full credit for this section, you must follow the instructions below
For the Post class, you must:
● Implement one test for getUpvoteCount()
● Implement one test for updateUpvoteCount()
● Implement one test for updateDownvoteCount() For the User class, you must:
● Implement one test for get Karma()
● Implement one test for addPost(Post post)
One simple test for each of the above methods is provided for you. Thus, you must have a total of two unit tests for each of the above methods. You may use the provided tests as inspiration for implementing your own test cases. As always, you are welcome (and encouraged) to add more test cases but, as long as you follow the above instructions, you will receive full credit for this part of the assignment.
Submission
VERY IMPORTANT: Please follow the instructions below carefully and make the exact submission format.
1. Go to Gradescope via Canvas and click on PA5.
2. Click the DRAG & DROP section and directly select the required files Post.java and User.java. Please make sure you DO NOT submit a zip, just the two files in one Gradescope submission. Make sure the names of the files are correct.
3. Following the previous step, our submission should look like the screenshot below. Click upload to submit your file.
4. You can resubmit an unlimited number of times before the due date. Your score will depend on your final submission, even if your former submissions have a higher score.
5. The autograder is for grading your uploaded files automatically. Make sure your code can compile on Gradescope. If your code fails to compile on gradescope you will receive zero points on ALL autograded components of your submission.
NOTE: The Gradescope Autograder you see is a minimal autograder. For this particular assignment, it will only show compilation results and the results of basic tests (from the write-up). After the assignment deadline, a thorough Autograder will be used to determine the final grade of the assignment. Thus, to ensure that you would receive full points from the thorough Autograder, it is your job to extensively test your code for correctness (make use of unitTests!)