Logistics

This is a paired assignment, so you should complete it with your assigned partner, if you have one, via paired programming. You should continue to work with your partner from homework 3. The whole time that you are working, you should both be present and actively working on the problem at hand. (Two brains, one keyboard.) Switch off the typing duties so that you each type for roughly half of the time.

You are able to get help from many sources as detailed in the collaboration policy.

This assignment is due on Friday Feb 2nd at 10pm. As with all assignments, you will have the opportunity to revise this assignment individually based on the feedback that you get.

Goals

To gain a better understanding of linked lists by implementing one that inserts values into sorted positions and maintains forward and backward pointers.

Setup and Requirements

Mount COURSES, download the HW4 starter code and move it to your StuWork/username folder.

Create a file Collaborations.txt and put in any help that you get on this assignment including sources that you reference and help from lab assistants or the prefect. Make sure to refer to the Collaboration page on what collaborations are allowed for homework assignments.

The code that you write for this assignment will build on top of the Country class that you worked with previously. I’ve provided my own version of it and the boilerplate code for reading in from a file and creating a Country.

Specification

For this assignment, you’ll make a new class, CountrySorterList that consists of a linked list that adds items in sorted order according to a previously set indicator and is able to provide the user with the minimum and maximum countries for the given indicator.

Comparator

If you were thinking after the Country Stats Displayer assignment that there has got to be a better way of sorting, you are right! In Java, there is an interface called the Comparator that focuses on allowing two objects of the same type to be compared easily. This is slightly different than the Comparable interface discussed and used in the book because it doesn’t assume that the class has an inherent order, and instead orders the objects of the class based on the user specified indicator. First you will create a comparator that will then be stored in your linked list later.

Create a new class CountryComparator that implements the Comparator interface for Country:

public class CountryComparator implements Comparator<Country> {

This class will consist of just two methods: 1) a constructor, and 2) the compare method that is required for a Comparator.

Constructor

Your comparator needs to store the indicator that it compares by. Create that instance variable and a constructor that takes in a value for indicator and sets the instance variable.

compare method

Next create a method compare that takes two Country objects as parameters. The Comparator’s compare method works similarly to the Comparable interface in that for two objects a and b, it returns:

  • -1 if a comes before b,
  • 0 if a and b could be in either order, and
  • 1 if b comes before a.

Your compare method should work the same based on the indicator chosen by the constructor.

You should test your CountryComparator by making a new one in the main(String[] args) method of CountryComparator.java with some test Country objects.

CountrySorterList

Now that you have an object for comparing two countries, let’s make a sorted linked list for your countries. Note that you are not allowed to use any built-in List classes or methods! The point of this homework is to understand linked lists by implementing your own.

Using CountryComparator

Your CountrySorterList should use an object of type CountryComparator to determine the order of the countries in the list.

add(Country newEntry)

You should create an add method that takes a Country object and puts it into the correct spot in the sorted list based on the comparator. The reading gives you a good start on this method and you can and should copy over the relevant code and credit it in your Collaborations.txt document. You will need to adapt the code to work with your CountryComparator though.

Double linking

You should adapt the starter code and reading code to have a doubly-linked list, which is a list where the Nodes have a link to the node before them, often called previous and you maintain a lastNode pointer as well as a firstNode pointer.

User interaction

The user should be able to specify the filename, number of top and bottom countries, and indicator of interest (in “”) that they want displayed via the command line interface, such as:

java CountrySorterList CountryDataset.csv 5 "Population Total"

which would then display the countries with the top 5 population totals and the bottom 5 population totals:

Lowest:
1. Tuvalu 0.01
2. Palau 0.02
3. Gibraltar 0.03
4. British Virgin Islands 0.03
5. Turks and Caicos Islands 0.04
------
Highest:
1. China 1364.8
2. India 1294.75
3. United States 318.37
4. Indonesia 254.95
5. Brazil 202.69

You can change the output formatting but need to have at least the names of the countries (the autograder will be checking that all required names are there and the human graders will be evaluating clearness of your output).

You should retrieve the top and bottom information efficiently, meaning that you should not have to loop all the way to the end of the list to get either the maximum or minimum countries. Instead, you should use the double linked nature of the list effectively.

README

As always, you should include a detailed README for this homework. It should include a brief overview of your project and a short example of how to run your program and see its interesting behavior.

Prompt

Include a discussion about why you are using the CountryComparator class instead of having Country implement the interface Comparable.

Assessment

To demonstrate proficiency, your program needs to:

  • Pass all tests on Gradescope
  • Follow the specifications for the command-line
  • Implemented CountrySorterList and CountryComparator correctly
  • Be object-oriented
  • Have a README with an overview, example, and response to the prompt
  • Have JavaDocs documentation for all public methods
  • Be somewhat well-styled

To demonstrate mastery, your program needs to:

  • Demonstrate proficiency
  • Use private variables correctly and effectively
  • Use the double-linked list effectively and efficiently
  • Be extremely well-styled and clear by choosing descriptive variable names and including useful comments
  • Have a thorough, well-styled README with thoughtful prompt response
  • Have clear and thorough documentation

Submission

Remember to update your Collaborations.txt file with any sources that you consulted.

Then upload all of your files to the Gradescope link on Moodle, at which point the autograder will run and let you know if your code works correctly. You are able to submit your code as many times as you wish before the deadline to fix any issues. If you have questions about what the autograder is telling you is wrong, please ask!