Java - TP2

Object Oriented Programming

Objectives

• Object-oriented programming (OOP)
• Java project structure
• Introduction to Maven
• Unit tests with JUnit

1 Before you start

When you’ve finished, don’t forget to delete your service.

After each part, create a commit and push your code to the remote repository.

1.1 Launch service VSCode Java

• Launch the service VScode-Java using this link.

1.2 Update your repo

if you haven’t done TP1 using your account

Follow the instructions in the introduction to TP1.

Important

During the first tutorial, you created a fork of the ENSAI-2A-Java-TP repository, i.e. you created a copy of this repository on GitHub.

The original repository has been updated, so you need to synchronise your fork with the latest version of the repository.

Choose one of these two possibilities to perform it :

• Using GitHub interface : sync on GitHub, and then clone on your VSCode
• Manually in a terminal : clone on your VSCode, and then sync using git commands

Using GitHub interface (easy way)

• Login to GitHub
• Open the fork of ENSAI-2A-Java-TP, you created at the first practical
• Click on the button Sync fork

In VSCode:

• Open a terminal and clone your own repo

In a terminal

• Open a terminal in VSCode
• Clone your repository
• Position yourself into the repo using cd <my_repo>
• Add the original repository as a remote (call it upstream)
  • git remote add upstream https://github.com/ludo2ne/ENSAI-2A-Java-TP.git
• Fetch the latest changes from upstream
  • git fetch upstream
• Make sure you’re on the branch main
  • git checkout main
• Merge the changes
  • git merge upstream/main
• Resolve any conflicts (if necessary)
• Push the updates to your fork
  • git push origin main

1.3 Open Folder

In VSCode :

• File > Open Folder > tp2

tp2 must be the root folder in your explorer.

2 Compile and run

Last time, you used the javac and java commands to compile and run your code.

This time, we’ll be working on a Maven project, so you’ll be able to use the following commands:

• mvn clean compile
  • Drop target folder, Download dependencies, Compile
• mvn exec:java
  • Run main method of Main class
• mvn test
  • Run unit tests

3 Exercice : Library management

The goal of this exercise is to simulate the management of a library where students can borrow books.

Steps :

• At first two classes are provided, Author and Book
• You also have a Main class which will be the entry point for your program (main method, compile, run)
• Create a class representing the library (attributes, methods)
• The application evolves: the library also offers magazines. Use OOP to upgrade your system (inheritance, abstract class)
• Set up features for loaning books and magazines

At the end of the tp, your code must implement this class diagram :

classDiagram
    class Library {
        -List~Item~ items
        -List~Loan~ activeLoans
        -List~Loan~ completedLoans
        +addIem()
        +displayItems()
        +getBooksByAuthor() List~Book~
        +loanItem() boolean
        +renderItem() boolean
        +findActiveLoanForItem() Loan
        +loadBooksFromCSV()
    }
    
    class Item {
        -String title
        -int year
        -int pageCount
    }
    
    class Book {
        -String isbn
        -Author author
    }
    
    class Magazine {
        -String issn
        -String issueNumber
    }

    class Person {
        -String name
        -int age
    }

    class Author {
        -String nationality
    }

    class Student {
        -int academicYear
        -boolean isClassDelegate
    }

    class Loan {
        -Item item
        -Student borrower
        -Date startDate
        -Date returnDate
    }

    Library  --  Item : has
    Library  --  Loan : manages
    Loan  --  Item : relates to
    Loan  --  Student : borrowed by
    Person <|-- Author : extends
    Person <|-- Student : extends
    Item <|-- Magazine : extends
    Item <|-- Book : extends
    Book  -- Author : written by

Note

• In Java, it’s conventional to declare all attributes as private.
• Constructors, getter and setters don’t appear on the diagram, nor do special methods (toString, equals)

3.1 Create the library

This class will represent the library and will have the following private attributes:

• name: A string that represents the name of the library
• books: A list of Books

and methods:

• a constructor
• addBook(Book book): Adds a book to the library’s collection
• displayBooks()
  • print all books of the library
  • use toString() method from Book class
  • or print a message if there is no book

---

• Create the Library class
• Add the method loadBooksFromCSV()
  • copy the code below
  • also add needed imports at the top of the class

loadBooksFromCSV

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;


    /**
     * Loads books from a CSV file and adds them to the library.
     * 
     * @param filePath The path to the CSV file containing book data.
     * @throws IOException If there is an error reading the file, an
     *                     {@link IOException} will be thrown.
     */
    public void loadBooksFromCSV(String filePath) {

        URL url = getClass().getClassLoader().getResource(filePath);

        try (BufferedReader br = new BufferedReader(new FileReader(url.getFile()))) {
            Map<String, Author> authors = new HashMap<>();
            String line;
            br.readLine(); // Skip the header line

            while ((line = br.readLine()) != null) {
                String[] data = line.split(",");

                if (data.length == 5) {
                    String isbn = data[0].trim();
                    String title = data[1].trim();
                    String authorName = data[2].trim();
                    int year = Integer.parseInt(data[3].trim());
                    int pageCount = Integer.parseInt(data[4].trim());

                    // Check if author already exists in the map
                    Author author = authors.get(authorName);
                    if (author == null) {
                        author = new Author(authorName);
                        authors.put(authorName, author);
                        System.out.println(author.toString());
                    }
                    Book book = new Book(isbn, title, author, year, pageCount);

                    this.addIem(book);
                }
            }
        } catch (

        IOException e) {
            System.err.println("Error reading the file: " + e.getMessage());
        }
    }

• Commit and push

3.2 Load books from file

All operations related to the library will be handled in the main class.

Update the main method of the Main class (Main.java):

• Create an instance of the Library
• Use the appropriate method to load books from the file books.csv
• Display all books

3.3 Magazine

The library is evolving and now includes magazines in addition to books. To accommodate this change, update your implementation while following object-oriented programming (OOP) principles

• Introduce an abstract class Item that will serve as the parent for both Book and Magazine
  • attributes: title, year, pageCount
• Modify class Book extends Item
• Create class Magazine extends Item
  • attributes: issn, issueNumber

In the Library class, replace:

• Attribute books by items
• Method displayBooks() by displayItems()

In the Main class:

• create and add two magazines to the library before calling displayItems()

3.4 Loans

The library system now needs to support book loans for students. To achieve this, update the implementation as follows:

• Create a class Student
  • attributes: name, age, academicYear, isClassDelegate
• Bonus: do you know of a class that has anything in common with the Student class? Implement
• Create a class Loan
  • attributes: student, item, startDate, returnDate (null at creation)
  • methods:
    • setReturnDate() to update the return date
    • toString() returning a String like “Item xxx borrowed by yyy.”
• Update the Library class adding two attributes:
  • activeLoans (A list of ongoing loans)
  • completedLoans (A list of returned loans)

3.5 Various methods

In the Library class create following methods:

• findActiveLoanForItem(Item item) -> Loan
  • Look if the item is present in active loans
  • Run unit tests
• getBooksByAuthor(Author author) -> ArrayList<Book>
  • write tests
• loanItem(Item item, Student student) -> boolean
  • Check if the item is available
  • Create a Loan and add it to activeLoans
• renderItem(Item item) -> boolean
  • Find the Loan if exists
  • Add a return date
  • Move an item from activeLoans to completedLoans
• displayActiveLoans() -> void

Feel free to use these methods in your main method.

4 End of the TP

• Commit and push
• Remove your service

Tip

If it’s too easy, you can have fun with https://adventofcode.com/

5 Java class

5.1 Example

Student.java

import java.util.ArrayList;

/**
 * Represents a student
 * Attributes : name, age, and a list of notes.
 */
public class Student {
    // -------------------------------------------------------
    // Attributes
    // -------------------------------------------------------
    private String name;
    private int age;
    private ArrayList<Double> notes;

    /**
     * Constructs a new Student object with the given name and age.
     * @param name The name of the student.
     * @param age The age of the student.
     */
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
        this.notes = new ArrayList<>();     // empty list
    }

    // -------------------------------------------------------
    // Getters and Setters (to access private attributes)
    // -------------------------------------------------------

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    /**
     * Sets the age of the student.
     * @param age The age to set. It should be greater than zero.
     * @throws IllegalArgumentException if the provided age is not greater than zero.
     */
    public void setAge(int age) {
        if (age <= 0) {
            throw new IllegalArgumentException("Age must be greater than zero.");
        }
        this.age = age;
    }
    
    // -------------------------------------------------------
    // Methods
    // -------------------------------------------------------

    /**
     * @return A string representation of the Student object.
     */
    @Override
    public String toString() {
        return "Student(" +
                "name='" + this.name + '\'' +
                ", age=" + this.age +
                ')';
    }

    /**
     * Adds a note to the student's list of notes.
     * @param note The note to be added.
     */
    public void addNote(double note) {
        this.notes.add(note);
    }

    /**
     * Computes the average note of the student.
     * @return The average note of the student.
     * @throws ArithmeticException if there are no notes present.
     */
    public double computeAverage() {
        if (this.notes.isEmpty()) {
            throw new ArithmeticException("Cannot compute average. No notes available.");
        }

        double sum = 0.0;
        for (double note : this.notes) {
            sum += note;
        }
        return sum / this.notes.size();
    }

    /**
     * Main method
     */
    public static void main(String[] args) {
        Student student = new Student("Eva", 20);
        student.addNote(17.5);
        student.addNote(12.0);
        student.addNote(20.0);
        
        System.out.println(student);
        System.out.println("Average Note: " + student.computeAverage());
    }
}

5.2 Template

ClassName.java

/**
 * Represents a ...
 */
public class ClassName {
    // -------------------------------------------------------
    // Attributes
    // -------------------------------------------------------
    private String attribute1;
    private int attribute2;

    /**
     * Constructs a new ...
     * @param parameter1 parameter1_description
     * @param parameter2 parameter2_description
     */
    public ClassName(String parameter1, int parameter2) {
        this.attribute1 = parameter1;
        this.attribute2 = parameter2;
    }


    // -------------------------------------------------------
    // Methods
    // -------------------------------------------------------

    /**
     * No parameter, return void
     */
    public void print_attribute1() {
        System.out.println(this.attribute1);
    }
    
    /**
     * Increment value of attribute2
     * A parameter, return void
     * @param increment increment
     */
    public void increment_attribute2(int increment) {
        this.attribute2 += increment;
    }
    
    /**
     * Checks if attribute2 is odd.
     *
     * @return true if attribute2 is odd, false otherwise.
     */
    public boolean isAttribute2Odd() {
        return attribute2 % 2 != 0;
    }


    /**
     * Main method
     */
    public static void main(String[] args) {

        ClassName c = new ClassName("", 0);
        c.increment_attribute2(5);
        System.out.println(c.isAttribute2Odd());
    }
}