OOP – Homework 10 – Linked Lists Solved

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Welcome to the final homework of CS 1331! Congratulations on making it this far. Up to this point, we’ve covered a wide breadth of topics – how to use the console, how to create classes, how to use inheritance and polymorphism, generics, and much more.
In this homework, you will gain exposure to another field of computing: the ways in which we store data.
For this assignment, we will be storing data in what is known as a Linked List.
You will implement a LinkedList using the given class and interface we’ve provided for you. But why are LinkedLists necessary, you might ask?
The Linked List
Linked Lists are meant to be an implementation of the abstract idea of a list.
A list is known as an abstract data type, also known as an ADT. ADT’s are nothing more than descriptions of a particular data structure – they tell us what the data structure can hold, and what operations we expect to be able to do, They do not provide implementations of these operations, nor do they tell us how data is physically held (do we use an array, a map, etc…). ADT’s are almost like a specific type of interface, in this regard.
For example, a list is an ADT whose elements are ordered and can be duplicates, and new data can be added at an index within the list.
Note that we haven’t yet stated how the data is being held, or how these addition operations are performed. We therefore provide concrete implementations of ADT’s – we write classes which implement these storage instructions and operations and then use these concrete classes to store and manipulate our data.
A LinkedList is one such implementation of the list idea. LinkedLists are composed of Nodes which hold one element of data and also a reference to the next Node in the list.
With these Nodes, it is possible to retrieve data at any index of the list, as well as add data, remove data, etc…
A diagram of this structure is embedded below.

Figure 1: Singly Linked List with Head Reference
The i-th element/piece of data of the list is stored in the i-th node. We keep a reference to the zero-th Node called head.
Solution Description
Now, you must create a new class called LinkedList which implements the interface SimpleList. You must use the Node class we have given you in order to construct your LinkedList.
LinkedList should also be able to store elements of any reference type using the Node class.
Instance Fields
LinkedList must have two private instance fields:
• a Node called head which is always the zero-th Node in the LinkedList.
• an int called size, which keeps track of how many nodes there are in the List. Feel free to add any other fields as you find helpful.
Note: please read the interface’s and class’ javadocs, etc… for more details.
Provided Files
We have provided two files – SimpleList.java and Node.java – an interface and class, respectively. Let’s
briefly go through these files.
1. void addAtIndex(T data, int index): takes in an element of T type, and an index, and adds the data to the LinkedList. Data must be added in the form of a Node containing the data.
• For addAtIndex, throw an IllegalArgumentException if the index is not valid (outside of [0,size] inclusive).
• Add the data to the list at the specified index.
• Before we call this method, consider a list with this data in this order: 0 -> 1 -> 2 -> 3. When we call list.addAtIndex(4, 2), we update our list like so: 0 -> 1 -> 4 -> 2 -> 3.
• NOTE: Make sure that the list is preserved and no data is lost during the adding!
• Be sure to update head and size when needed (for example, would adding at the back change head?).
2. T get(int index): takes in an index, and returns the appropriate data. Also swaps data of the i-th node with the data of the (i-1)(th) node. Read below for more details.
• If the list is empty, throw a NoSuchElementException.
• Throw an IllegalArgumentException if the index is not valid (outside of [0, size-1] inclusive).
– Please implement these checks in the order they have been presented. If a list is empty, there’s no need to worry about an IllegalArgumentException, for example.
• We want to do something very interesting with this method. When we get the data out of the index-th node, we want to swap the data of the index-th node with the data of the (index-1)-th node. That is, let’s say there were three nodes (indexed as 0, 1, 2, where 0 is the head), and if I got the data located at index 1, I want 0’s data and 1’s data to be swapped. Swap the data.
• Graphically, this is represented as so. If I have a list with data in this order: 0 -> 1 -> 2, list.get(1) will return 1, and the list is updated as such: 1 -> 0 -> 2.
• What happens if the data is at the head, however? Make sure to account for this case (no swaps are needed).
3. boolean contains(T data): takes in an element of data, and returns true if the element is contained in the LinkedList, or false if it isn’t.
4. boolean isEmpty(): Returns true the LinkedList is empty, false otherwise.
5. T removeAtIndex(int index): takes in an index, and returns the data located at the index-th node. Fully removes index-th node from the LinkedList.
• If the list is empty, throw a NoSuchElementException.
• If the index is invalid, then throw an IllegalArgumentException.
– Please implement these checks in the order they have been presented. If a list is empty, there’s no need to check the index, for example.
• Given an index that is valid ([0, size – 1]), get/save the data of the Node.
• Assuming everything is valid, remove the index-th Node fully from the list. For example, if I had a list with data in this order: 0 -> 1 -> 2 -> 3, and I invoked list.removeAtIndex(2), my final list should be: 0 -> 1 -> 3, and “2” should be returned.
• Return the data that you saved.
• NOTE: Make sure that the list is preserved after removal, and no additional data is lost!
• NOTE: Make sure head and size are changed appropriately (if I remove the zero-th Node, for example, from the list, how is head affected? What does head point to now?).
6. int size(): returns the size of the LinkedList.
7. T[] toArray(): returns an array which is of the same length as the LinkedList, but only contains the data of the LinkedList, not its nodes. NOTE: Make sure the data in the array is in the same order as the LinkedList.
Node is a generically typed class – it can hold data of any reference type. It contains these two fields:
• data – some data of type T.
• next – another Node of type T.
Both of these fields are private, so we’ve included getter and setter methods for you.
Allowed Imports
To prevent trivialization of the assignment, you can only import java.util.NoSuchElementException, as you’ll need to throw this exception in certain situations.
No other imports are allowed. If you have questions about what to import or not import, feel free to make a post in Piazza.
Feature Restrictions
There are a few features and methods in Java that overly simplify the concepts we are trying to teach. For that reason, do not use any of the following in your final submission:
• var (the reserved keyword)
• System.arraycopy
• System.exit
[100] LinkedList
• [5] LinkedList() – the constructor for a LinkedList.
– [5] Constructs the LinkedList correctly – head is set to null, and size is set to 0.
• [25] addAtIndex(T data, int index)
– [5] IllegalArgumentException is thrown if the index provided is invalid.
– [15] A Node containing data is added to the LinkedList at the correct location, and is now the index-th Node in the LinkedList. All data is preserved correctly after the add. This is very important.
∗ Seriously, there’s a reason this entire method is worth 25 points. There’s a few major cases to handle in this method. Think and code carefully. – [5] head and size are changed appropriately.
• [10] get(int index)
– [1] If the list is empty, throw a NoSuchElementException.
– [1] If index is not within bounds, throw an IllegalArgumentException.
∗ Please implement the above checks in the same order they have been presented.
– [2] Get/return the data at the index-th Node. – [4] Successfully swaps data at indexed node with the data of the node right before.
(Handles all cases).
– [2] All data is preserved; no data is lost.
• [10] contains(T data)
– [5] Returns true if data is indeed in the LinkedList.
– [5] Returns false if data is indeed not in the LinkedList.
• [5] isEmpty()
– [5] 5 free points is nice, right? Return true if true, false if false.
• [25] removeAtIndex(int index)
– [2.5] If list is empty, then throw a NoSuchElementException.
– [2.5] If index is invalid, then throw an IllegalArgumentException.
∗ Please implement these checks in the order they have been presented.
– [5] Data of the index-th Node is returned.
– [10] The index-th Node is removed from the LinkedList. All data/Nodes (except for the removed Node) are preserved. This is very important. – [5] size and head are changed appropriately.
• [10] size() (the method)
– [10] size() (the method), returns the size of the List.
• [10] toArray()
– [3] An array of T[] is returned.
– [3] The array is of the same size as the LinkedList.
– [4] The array contains all the data of all the Nodes in the same order as the LinkedList.
Collaboration Statement
I worked on the homework assignment alone, using only course materials.
In order to help learn course concepts, I worked on the homework with [give the names of the people you worked with], discussed homework topics and issues with [provide names of people], and/or consulted related material that can be found at [cite any other materials not provided as course materials for CS 1331 that assisted your learning].
Allowed Collaboration
• What general strategies or algorithms you used to solve problems in the homeworks
• Parts of the homework you are unsure of and need more explanation
• Online resources that helped you find a solution
• Key course concepts and Java language features used in your solution
Checkstyle and Javadocs
You must run checkstyle on your submission. The checkstyle cap for this assignment is 20 points. Review the style guide and download the checkstyle jar. Run checkstyle on your code like so:
$ java -jar checkstyle-6.2.2.jar -a *.java Audit done. Errors (potential points off):
Make sure to include the -a flag included for testing both checkstyle and javadocs
The message above means there were no Checkstyle or javadoc errors. If you had any errors, they would show up above this message, and the number at the end would be the points we would take off (limited by the checkstyle cap mentioned above). The Java source files we provide contain no Checkstyle errors. In future homeworks we will be increasing this cap, so get into the habit of fixing these style errors early!
Depending on your editor, you might be able to change some settings to make it easier to write style-compliant code. See the customization tips page for more information.
To submit, upload the files listed below to the corresponding assignment on Gradescope:
• LinkedList.java
Make sure you see the message stating “HW## submitted successfully”. From this point, Gradescope will run a basic autograder on your submission as discussed in the next section.
Gradescope Autograder
For each submission, you will be able to see the results of a few basic test cases on your code. Each test typically corresponds to a rubric item, and the score returned represents the performance of your code on those rubric items only. If you fail a test, you can look at the output to determine what went wrong and resubmit once you have fixed the issue.
The Gradescope tests serve two main purposes: 1) Prevent upload mistakes (e.g. non-compiling code)
2) Provide basic formatting and usage validation
In other words, the test cases on Gradescope are not comprehensive. Be sure to thoroughly test your code by considering edge cases and writing your own test files. You also should avoid using Gradescope to compile and run your code; you can do that locally on your machine.
Important Notes (Don’t Skip)
• Non-compiling files will receive a 0 for all associated rubric items
• Test your code in addition to the basic checks on Gradescope
• Submit every file each time you resubmit
• Ensure you pass all “FORMAT:” tests
• Read the “Allowed Imports” and “Restricted Features” to avoid losing points
• Check on Piazza for a note containing all official clarifications


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