Homework #2: Circular Singly-Linked List Solution

Important




There are general homework guidelines you must always follow. If you fail to follow any of the following guidelines you risk receiving a 0 for the entire assignment.







1. All submitted code must compile under JDK 8. 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 sig- natures.




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 Array List 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 must submit your source code, the .java files, not the compiled .class files.




8. 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.







Circular Singly-Linked List




You are to code a circular singly-linked list with a head reference. A linked list is a collection of nodes, each having a data item and a reference pointing 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.




It will use the default constructor (the one with no parameter) which is automatically provided by Java. Since instance variables are automatically assigned default values, it is not necessary to explicitly set them, so do not write your own constructor.




As an additional note, your circular implementation doesn’t have a tail reference, but it is still pos- sible 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.




Nodes




The linked list consists of nodes. A class LinkedListNode is provided to you. LinkedListNode has setter and getter 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. See the javadocs for more details.







Removing




Removing, just like adding, can be done from the front, the back, or anywhere in your linked list. In addition, you will also be coding a method to remove the last instance of a piece of data. When removing from the front, the first node should be removed in such a way that the last node points to the new front of the list (mind the efficiency!). When removing from the back, the last node should be removed and have the new last node point to the head. When removing from the middle, the node before the removed node should point to the next node of the removed node. 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 since the node will be Garbage Collected eventually.




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 opera- tions 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()




• T removeLastOccurrence(T data) ⇒ boolean removeLastOccurrence(Object data)







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
removeLastOccurrence
10pts
get
10pts
toArray
6pts
clear
5pts
isEmpty
4pts
Other:


Checkstyle
10pts
Efficiency
15pts
Total:
100pts
Keep in mind that add functions are necessary to test other functions, so if an add doesn’t work, remove tests might fail as the items to be removed were not added correctly. Additionally, the size function is used many times throughout the tests, so if the size isn’t updated correctly or the method itself doesn’t work, many tests can fail.




A note on JUnits




We have provided a very basic set of tests for your code, in LinkedListStudentTests.java. These tests do not guarantee the correctness of your code (by any measure), nor do they guarantee you any grade. You may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as a list of JUnits other students have posted on the class Piazza.




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.




Style and Formatting




It is important that your code is not only functional but is also written clearly and with good style. We will be checking your code against a style checker that we are providing. It is located on Canvas, under Files, along with instructions on how to use it. We will take off a point for every style error that occurs. If you feel like what you wrote is in accordance with good style but still sets off the style checker please email Tim Aveni (tja@gatech.edu) with the subject header of “[CS 1332] CheckStyle XML”.




Javadocs




Javadoc any helper methods you create in a style similar to the existing Javadocs. If a method is overridden or implemented from a superclass or an interface, you may use @Override instead of writing Javadocs. Any Javadocs you write must be useful and describe the contract, parameters, and return value of the method; random or useless javadocs added only to appease Checkstyle will lose points.




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 mes- sage 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




You may not use these in your code at any time in CS 1332.







• 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.







Provided




The following file(s) have been provided to you. There are several, but we’ve noted the ones to edit.







1. SinglyLinkedList.java

This is the class in which you will implement the SinglyLinkedList. The instructions and effi- ciency of each method are mentioned in the javadocs. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.




2. LinkedListNode.java

This class represents a single node in the linked list. It encapsulates data and the next reference.

Do not alter this file.




3. LinkedListStudentTests.java

This is the test class that contains a set of tests covering the basic operations on the SinglyLinkedList 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). Please make sure the filename matches the filename(s) below, and that only the following file(s) are present. If you make resubmit, make sure only one copy of the file is present in the submission.




After submitting, double check to make sure it has been submitted on Canvas and then download your uploaded files to a new folder, copy over the support files, recompile, and run. It is your responsibility to re-test your submission and discover editing oddities, upload issues, etc.







1. SinglyLinkedList.java