1. Playing with Objects is Still Fun

Worth: 5%
DUE: Monday July 7, 2025, 11:55pm; submitted on MOODLE.

1.1. Task

The goal is to create a collection of Country objects. The collection, called a CountryCatalogue, will provide functionality to store (add/remove) the Country objects in addition to making inquiries about the data in the collection.

Effectively, the idea is to recreate your assignment 4 written in Python from the previous course, but in Java. Be aware that the assignment is not identical and the requirements outlined here will be what is required.

You will

Create a Country class to store details about a country
Create a CountryCatalogue class
- Provide a way to add and remove Country objects
- Search through the catalogue
- Ask questions about the data in the catalogue
- Filter data in the catalogue
Test the implementation with the provided test classes
Use the classes to build a CountryCatalogue
Read data from a file
Write data to a file

1.2. Provided Files

You are provided with

A nearly empty Country.java file to be completed
A nearly empty CountryCatalogue.java file to be completed
A completed Asn1.java file with a main method and some testing code
A csv file called country_data.csv containing information about countries to be added to a CountryCatalogue
A completed CountryTest.java file containing unit tests for the Country class
A completed CountryCatalogueTest.java file containing unit tests for the CountryCatalogue class
All of this can be downloaded from here
- This is a compressed IntelliJ project
- Just unzip, put it where you want on your computer, and you should be able to open this project through IntelliJ

Warning

When opening the project, IntelliJ may mention a missing JDK. If this is the case, simply select the download link in the notification to download and install the missing JDK.

1.3. Part 0 — Read the Assignment

Read the assignment description in its entirety before starting.

1.4. Part 1 — Country

The Country class will store data related to the country it represents. The data stored will be the country name, population, area, and continent. The CountryCatalogue class described in part 2 will store instances of the Country class.

Write a constructor for the Country class that takes four (4) parameters to be stored as class fields
- name — type String
- continent — type String
- population – type long
- area — type double
Note

Notice that the type for population is a long. One may be tempted to simply use an int, but the int type has a limitation.

In Java, int values are stored in four bytes (4B)/32 bits (32b), which means the number of unique values the int can represent is \(2^{32}\), which is \(4,294,967,296\). More specifically, int values can store values between \(-2,147,483,648\) and \(+2,147,483,647\). Since the population of continents can exceed two billion, the int is not going to work.

The simplest solution to this problem is to make use of the long type. long values are just like int values, but are stored in eight bytes (8B)/64 bits (64b). This means a long can represent \(2^{64}\) (\(1.84^{19}\)) unique values.
Write accessor/getter methods for each class field
- Call these methods getX where X is the name specific field
- For example, getArea would return the field area
Write a method to calculate and return the population density (population/area)
- Call this method populationDensity
- With floating point numbers (doubles included), division by zero results in a special value — Infinity
- If this method is called on a Country object with an area of zero, it should return Infinity
- In other words, this method should not perform any special check for area being zero
Write a toString method to return a string following the pattern ClassName(field=value, field=value, ... )
- For example — Country(name=Canada, continent=North America, population=34207000, area=9976140.00)
- Mind the format of the string — the area field has two decimal places
  Consider using the format method from the String class
Write an equals and hashCode method
- Two Country objects will be considered equal if all fields match
- Be mindful of how the double values are compared
Run the unit tests to ensure the Country class works properly
- It may be necessary to add JUnit to the class path, as described in the testing topic
Warning

Be sure to use JUnit 5. If you use JUnit 4, the tests will not work. Further, if you select JUnit 4 by accident, changing the project to use JUnit 5 can be difficult.

1.5. Part 2 — Country Catalogue

The CountryCatalogue class holds references to Country objects. Additionally, the CountryCatalogue provides functionality to add and remove Country objects to itself and ask questions about the data. The CountryCatalogue is effectively a list keeping track of the Country objects with additional functionality.

Although the description of this class is provided with an order and each part is numbered, one should feel free to complete the methods in any order they see fit. Additionally, feel free to write and use additional private methods as needed.

The CountryCatalogue class will need two fields

size — an int to keep track of the number of Country objects in the catalogue

catalogue — an array of Country objects

The class will also have two static constants

An int called NOT_FOUND that is set to -1

This constant serves as a nice way to indicate, with a sentinel value, that something was not found

An int for this class called DEFAULT_CAPACITY that should be set to 10

This will be used as a starting size for the catalogue array if none is specified upon creation

Write a toString method that returns a String representation of the CountryCatalogue

The String should be an aggregate of the String representations of the Country objects within the CountryCatalogue

Each Country object’s String representation should be on its own line

For example
Country(name=Nigeria, continent=Africa, population=186987563, area=912134.45)
Country(name=Mexico, continent=North America, population=128632004, area=1969230.76)
Country(name=Egypt, continent=Africa, population=93383574, area=1000000.00)
Country(name=France, continent=Europe, population=64668129, area=541656.76)
Country(name=Italy, continent=Europe, population=59801004, area=300000.00)

Uncomment out the provided equals and hashCode methods
- These are provided since writing equals for collections and testing them can be tricky
Run the unit tests to ensure the Country class works properly

1.6. Part 3 — File IO and Using Classes

A complete main method has been provided to you within the Asn1 class. Take your time to read over the code carefully and make sense of what it is doing. You are not required to make any changes to this code, but you are required to understand it and how it works.

The first portion of main loads data from a file, parses it, and then uses the data to create Country objects to add to a CountryCatalogue.

The next portion simply alters the contents of the CountryCatalogue object and the third part queries the CountryCatalogue for some details.

The last portion of main creates a new CountryCatalogue by filtering the existing CountryCatalogue. The details of the Country objects within the new filtered CountryCatalogue are added to a string that is then ultimately saved to a csv file.

There are no unit tests for main. To test it, simply run it and check if it works as expected.

Note

In the Python implementation in the previous course, most file IO was done by reading/writing a single line at a time from/to the file. It is entirely possible to read/write one line at a time in Java, but here, when reading from a file, notice that the whole contents of the file is read as a single string and then parsed. Similarly, when writing to a file, the whole string is created before it is written to the file as a single string.

Note

The functions Files.readString and Files.writeString used for file IO may throw IOExceptions. Notice, however, that these calls are not wrapped with try/catch. This is because main includes throws IOException in its signature, as described in the Java vs. Python topic’s IO Section.

1.7. Part 4 — Testing

You might need to add JUnit to the classpath for the project, as described in the testing topic.

You may have already verified the correctness of your Country and CountryCatalogue classes by running their test classes. If not, do it!

If you have, for good measure, re-run all the tests provided to you. If they all pass, you should be pretty confident that you have everything working correctly.

There are no tests provided for the Asn1 class, but that’s nothing to worry about. You can get a sense that it is working correctly by running the main method and checking that everything worked as expected.

1.8. Some Hints

Work on one method at a time
Get each method working perfectly before you go on to the next one
Test each method as you write it
- This is a really nice thing about programming; you can call your methods and see what result gets returned
- Mentally test before you even write — what does this method do? What problem is it solving?
If you need help, ask
- Drop by office hours

1.9. Some Marking Details

Warning

Just because your program produces the correct output, that does not necessarily mean that you will get perfect, or even that your program is correct.

Below is a list of both quantitative and qualitative things we will look for:

Correctness?
Did you follow instructions?
Comments?
Variable Names?
Style?
Did you do just weird things that make no sense?

1.10. What to Submit to Moodle

Make sure your NAME, SCHOOL EMAIL, and STUDENT NUMBER appear in a comment at the top of the classes
Submit your completed .java files to Moodle
- Country.java and CountryCatalogue.java
- Do not submit the Asn1.java file
- Do not submit the .csv files
- Do not submit the .class files
- Do not compress the files

Warning

Verify that your submission to Moodle worked. If you submit incorrectly, you will get a 0.

1.11. Assignment FAQ

See the general FAQ