Description
ArrayList
You are to code an ArrayList, which is a list data structure backed by an array where all of the data is
contiguous and aligned with index 0 of the array.
The ArrayList must follow the requirements stated in the javadocs of each method you must implement.
A constructor stub is provided for you to fill out.
Capacity
The starting capacity of the ArrayList should be the constant INITIAL CAPACITY defined in ArrayList.java.
Reference the constant as-is. Do not simply copy the value of the constant. Do not change the constant.
If, while adding an element, the ArrayList does not have enough space, you should regrow the backing
array to twice its old capacity. Do not regrow the backing array when removing elements.
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. When adding to the front or the middle of the
list, subsequent elements must be shifted back one position to make room for the new data. 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. When removing from the front or from the middle of the list, the element should be
removed and all subsequent elements should be shifted forward by one position. When removing from
the back, the last element should be set to null in the array. All unused positions in the backing
array must be set to null. See the javadocs for more details.
Amortized Efficiency
The efficiency of methods and algorithms in this course is often analyzed using a “per operation” analysis.
That is, what is the worst this algorithm can do on any one instance? However, there are times where this
type of analysis is unrealistically pessimistic. For example, in this homework, the addToBack() method
is O(1) for the most part except in the case of resizing, which is O(n). However, a resize operation is
rare enough that it’d be misleading to say that the method is O(n).
In cases like this, we use an amortized analysis. This type of analysis adds up the cost of a series of operations and then averages the cost. Here, the resize step is O(n), but since we double the
capacity whenever the array gets full, we’ve put off resizing for another n add operations. So, putting
that together with the common, cheap O(1) operations, we get O(1) using this analysis. Whenever this
type of analysis is used, we will prefix the Big-O with the word amortized.
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.
Value equality is used when using the .equals() method. Here, the definition of equality is custom
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Homework 1: ArrayList Due: See Canvas
made for the object. For example, in that Person example above, we may want two objects to be considered equal 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 ArrayList
class. 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) ⇒ no explicit method
• addToBack(T data) ⇒ add(T data)
• removeAtIndex(int index) ⇒ remove(int index)
• removeFromFront() ⇒ no explicit method
• removeFromBack() ⇒ no explicit method
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Homework 1: ArrayList Due: See Canvas
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 15pts
addToFront 11pts
addToBack 11pts
removeAtIndex 11pts
removeFromFront 7pts
removeFromBack 7pts
get 6pts
isEmpty 3pts
clear 4pts
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. ArrayList.java
This is the class in which you will implement the ArrayList. Feel free to add private helper
methods but do not add any new public methods, inner/nested classes, instance variables, or static variables.
2. ArrayListStudentTest.java
This is the test class that contains a set of tests covering the basic operations on the ArrayList
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. The only exception is that Canvas will automatically append
a -n depending on the submission number to the file name(s). This is expected and will be handled by
the TAs when grading as long as the file name(s) before this add-on matches what is shown below. If
you resubmit, be sure only one copy of each file is present in the submission. 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 Canvas. 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. ArrayList.java
