CS1332 Homework 2 Solution

1. All submitted code must compile under JDK 11. This includes unused code, so don’t submit extra files that don’t compile. Any compile errors will result in a 0.
2. Do not include any package declarations in your classes.
3. Do not change any existing class headers, constructors, instance/global variables, or method signatures. For example, do not add throws to the method headers since they are not necessary.
4. Do not add additional public methods.
5. Do not use anything that would trivialize the assignment. (e.g. Don’t import/use java.util.ArrayList for an ArrayList assignment. Ask if you are unsure.)
6. Always be very conscious of efficiency. Even if your method is to be O(n), traversing the structure multiple times is considered inefficient unless that is absolutely required (and that case is extremely rare).
7. You are expected to implement all of the methods in this homework. Each unimplemented method will result in a deduction.
8. You must submit your source code, the .java files, not the compiled .class files.
9. Only the last submission will be graded. Make sure your last submission has all required files. Resubmitting will void all previous submissions.
10. After you submit your files, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong files.
Style and Formatting
Javadocs
Vulgar/Obscene Language
Any submission that contains profanity, vulgar, or obscene language will receive an automatic zero on the assignment. This policy applies not only to comments/javadocs, but also things like variable names. Exceptions
When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. “Error”, “BAD THING HAPPENED”, and “fail” are not good messages. The name of the exception itself is not a good message. For example:
Bad: throw new IndexOutOfBoundsException(‘‘Index is out of bounds.’’);
Good: throw new IllegalArgumentException(‘‘Cannot insert null data into data structure.’’);
Generics
If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList<Integer>() instead of new LinkedList(). Using the raw type of the class will result in a penalty.
Forbidden Statements
• package
• System.arraycopy()
• clone()
• assert()
• Arrays class
• Array class
• Thread class
• Collections class
• Collection.toArray()
• Reflection APIs
• Inner or nested classes
• Lambda Expressions
• Method References (using the :: operator to obtain a reference to a method)
If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework files, just ask.
Debug print statements are fine, but nothing should be printed when we run your code. We expect clean runs - printing to the console when we’re grading will result in a penalty. If you submit these, we will take off points.
JUnits
If you need help on running JUnits, there is a guide, available on Canvas under Files, to help you run JUnits on the command line or in IntelliJ.
CircularSinglyLinkedList
You are to code a CircularSinglyLinkedList with a head reference. A linked list is a collection of nodes, each having a data item and references to other nodes. In a CircularSinglyLinkedList, each node has a reference to the next node. Since it must be circular, the next reference for the last node in this list will point to the head node. As a special case, this means that in a one node list, the head node will point to itself.
Do not use a phantom node to represent the start or end of your list. A phantom or sentinel node is a node that does not store data held by the list and is used solely to indicate the start or end of a linked list. If your list contains n elements, then it should contain exactly n nodes.
The CircularSinglyLinkedList must follow the requirements stated in the javadocs of each method you must implement. Your linked list implementation will use the default constructor (the one with no parameters) which is automatically provided by Java. Do not write your own constructor.
As an additional note, your circular implementation doesn’t have a tail reference, but it is still possible to efficiently add and remove from the head as well as add to the back in O(1) time. However, it is still not possible to remove from the back in O(1) time unless the linked list is doubly-linked.
The examples below demonstrate what the CircularSinglyLinkedList should look like at various states.
Size 0:

Size 1:

Size 4:

Nodes
The linked list consists of nodes. A class CircularSinglyLinkedListNode is provided to you. This class has getter and setter methods to access and mutate the structure of the nodes.
Adding
You will implement three add() methods. One will add to the front, one will add to the back, and one will add to anywhere in the list given a specific index. See the javadocs for more details.
Removing
You will also implement three remove() methods - from the front, the back, or anywhere in the list given a specific index. Make sure that there is no longer any way to access the removed node so that the node will be garbage collected. See the javadocs for more details.
Garbage Collection
Java will automatically mark objects for garbage collection based on whether there is any means of accessing the object. In other words, if we want to remove a node from the list, we must remove all references to that node. What the next reference of that node points to doesn’t particularly matter. As long as no references can reach the node, the node will be garbage collected eventually. Equality
There are two ways of defining objects as equal: reference equality and value equality.
Reference equality is used when using the == operator. If two objects are equal by reference equality, that means that they have the exact same memory locations. For example, say we have a Person object with a name and id field. If you’re using reference equality, two Person objects won’t be considered equal unless they have the exact same memory location (are the exact same object), even if they have the same name and id.
Keep in mind which makes more sense to use while you are coding. You will want to use value equality in most cases in this course when comparing objects. Notable cases where you’d use reference equality include checking for null or comparing primitives (in this case, it’s just the == operator being overloaded).
Differences between Java API and This Assignment
Some of the methods in this assignment are called different things or don’t exist in Java’s LinkedList class. Additionally, Java’s built in LinkedList is a Doubly-Linked List, so the efficiency of some operations will differ. This won’t matter until you tackle coding questions on the first exam, but it’s something to be aware of. The list below shows all methods with a different name and their Java API equivalent if it exists. The format is assignment method name ⇒ Java API name.
• addAtIndex(int index, T data)⇒add(int index, T data)
• addToFront(T data)⇒addFirst(T data)
• addToBack(T data)⇒add(T data) or addLast(T data)
• removeAtIndex(int index)⇒remove(int index)
• removeFromFront()⇒poll() or pollFirst()
• removeFromBack()⇒pollLast()
Grading
Here is the grading breakdown for the assignment. There are various deductions not listed that are incurred when breaking the rules listed in this PDF and in other various circumstances.
Methods:
addAtIndex 10pts
addToFront 5pts
addToBack 5pts
removeAtIndex 10pts
removeFromFront 5pts
removeFromBack 5pts
get 10pts
isEmpty 4pts
clear 5pts
removeLastOccurrence 10pts
toArray 6pts
Other:
Checkstyle 10pts
Efficiency 15pts
Total: 100pts
Provided
The following file(s) have been provided to you. There are several, but we’ve noted the ones to edit.
1. CircularSinglyLinkedList.java
This is the class in which you will implement the CircularSinglyLinkedList. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
2. CircularSinglyLinkedListNode.java
This class represents a single node in the linked list. It encapsulates the data and the next reference. Do not alter this file.
3. CircularSinglyLinkedListStudentTest.java
This is the test class that contains a set of tests covering the basic operations on the CircularSinglyLinkedList class. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases.
Deliverables
You must submit all of the following file(s). Make sure all file(s) listed below are in each submission, as only the last submission will be graded. Make sure the filename(s) matches the filename(s) below, and that only the following file(s) are present. If there are multiple files, do not zip up the files before submitting; submit them all as separate files.
Once submitted, double check that it has uploaded properly on Gradescope. To do this, download your uploaded file(s) to a new folder, copy over the support file(s), recompile, and run. It is your sole responsibility to re-test your submission and discover editing oddities, upload issues, etc.
1. CircularSinglyLinkedList.java