TD1 — VSCodium, Maven & First Java Classes

← Part 1 Overview

S7 Inf A3 — Java for Graphical and Mobile Programming
Stéphane Derrode — Centrale Lyon
Part 1 — Java Fundamentals
Duration: 2h · Pair or individual work

Objectives

By the end of this session you will be able to:

Create and run a Maven project in VSCodium
Write Java classes with private fields, constructors, getters and setters
Instantiate objects, call methods, and use toString()
Understand the difference between == and .equals()
Work with arrays of objects

Part 0 — Environment Setup

This part should already be done before the session.
Follow the VSCodium & Maven Setup Tutorial available on the course website. It walks you through installing JDK 17, Maven, VSCodium, and the Java Extension Pack step by step.

If you have any problem with installation, come 10 minutes early and we will sort it out.

Quick check — open a terminal inside VSCodium and verify:

java -version     # openjdk 17.x.x
mvn -version      # Apache Maven 3.x.x

Part 1 — Create the Maven Project (10 min)

1.1 Create the project

In VSCodium, press Ctrl+Shift+P → type Maven: Create Maven Project → select:

Archetype: maven-archetype-quickstart, version 1.5
Group Id: com.s7infa3
Artifact Id: td1

Then File ▸ Open Folder… and select the td1/ folder that was just created.

1.2 Configure Java 17

Replace the content of pom.xml with:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.s7infa3</groupId>
  <artifactId>td1</artifactId>
  <version>1.0</version>
  <properties>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
</project>

Save (Ctrl+S). Then open src/main/java/com/s7infa3/App.java, click ▶ Run above main() — you should see Hello World!.

Part 2 — Class `Voiture` (45 min)

2.1 UML specification

┌──────────────────────────────────────────┐
│                Voiture                   │
├──────────────────────────────────────────┤
│ - puissance   : int                      │
│ - estDemarree : boolean                  │
│ - vitesse     : double                   │
├──────────────────────────────────────────┤
│ + Voiture(int p)                         │
│ + Voiture()                              │
│ + Voiture(int p, boolean d, double v)    │
│ + deQuellePuissance() : int              │
│ + getVitesse() : double                  │
│ + isEstDemarree() : boolean              │
│ + demarre() : void                       │
│ + arrete() : void                        │
│ + accelere(double v) : void              │
│ + equals(Object obj) : boolean           │
│ + toString() : String                    │
└──────────────────────────────────────────┘

2.2 Behaviour rules

Method	Behaviour
`Voiture(int p)`	If `p > 0`, `puissance = p`; otherwise `puissance = 5`. Always: `estDemarree = false`, `vitesse = 0.0`
`Voiture()`	Delegate to `Voiture(5)` using `this(5)`
`demarre()`	Sets `estDemarree = true`
`arrete()`	Sets `estDemarree = false` and `vitesse = 0.0`
`accelere(double v)`	Only if `estDemarree == true`: `vitesse += v + 25`
`equals(Object obj)`	Two `Voiture` are equal if they have the same `puissance`
`toString()`	Returns `"Voiture[p=4, demarree=true, v=124.8]"`

2.3 Skeleton to complete

Create src/main/java/com/s7infa3/Voiture.java:

package com.s7infa3;

public class Voiture {

    // TODO: declare the 3 private fields

    public Voiture(int p) {
        // TODO
    }

    public Voiture() {
        this(5); // delegates to Voiture(int)
    }

    public Voiture(int p, boolean d, double v) {
        // TODO
    }

    public int     deQuellePuissance() { /* TODO */ return 0; }
    public double  getVitesse()        { /* TODO */ return 0; }
    public boolean isEstDemarree()     { /* TODO */ return false; }

    public void demarre()          { /* TODO */ }
    public void arrete()           { /* TODO */ }
    public void accelere(double v) { /* TODO */ }

    @Override
    public boolean equals(Object obj) {
        // TODO: true if obj is a Voiture with same puissance
        return false;
    }

    @Override
    public String toString() {
        // TODO: "Voiture[p=4, demarree=true, v=124.8]"
        return "";
    }
}

2.4 Test in `App.java`

Replace App.java with the following and verify every printed value:

package com.s7infa3;

public class App {
    public static void main(String[] args) {

        // Basic usage
        Voiture maClio = new Voiture(4);
        maClio.demarre();
        maClio.accelere(99.8);
        System.out.println(maClio);
        // Voiture[p=4, demarree=true, v=124.8]

        // Invalid power → defaults to 5
        Voiture defaut = new Voiture(-10);
        System.out.println(defaut.deQuellePuissance()); // 5

        // accelere() has no effect if not started
        Voiture immobile = new Voiture(6);
        immobile.accelere(50.0);
        System.out.println(immobile.getVitesse());      // 0.0

        // arrete()
        maClio.arrete();
        System.out.println(maClio);
        // Voiture[p=4, demarree=false, v=0.0]

        // == vs equals()
        Voiture saPolo = new Voiture(4);
        System.out.println(maClio == saPolo);           // false (different objects)
        System.out.println(maClio.equals(saPolo));      // true  (same puissance)

        // Three-argument constructor
        Voiture v2 = new Voiture(28, true, 0.0);
        System.out.println(v2);
        // Voiture[p=28, demarree=true, v=0.0]
    }
}

Part 3 — Array of Objects: class `Parc` (25 min)

A Parc manages a fixed-size fleet of Voiture objects using a plain array (not ArrayList — that is CM2).

3.1 Specification

Create src/main/java/com/s7infa3/Parc.java:

Member	Description
`Parc(int capacity)`	Creates an array of `capacity` slots (all `null` initially)
`add(Voiture v)`	Adds `v` to the next free slot; silently ignores if full
`size()`	Returns the number of vehicles currently stored
`getAt(int i)`	Returns the vehicle at index `i`; throws `IllegalArgumentException` if out of range
`demarrerTout()`	Calls `demarre()` on every stored vehicle
`toString()`	Returns one vehicle per line

3.2 Skeleton

package com.s7infa3;

public class Parc {
    private Voiture[] fleet;
    private int count;

    public Parc(int capacity) {
        // TODO
    }

    public void add(Voiture v) {
        // TODO: add only if count < fleet.length
    }

    public int size() { /* TODO */ return 0; }

    public Voiture getAt(int i) {
        // TODO: throw IllegalArgumentException if i < 0 or i >= count
        return null;
    }

    public void demarrerTout() {
        // TODO: loop over the count stored vehicles
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        // TODO: append each vehicle + newline
        return sb.toString();
    }
}

3.3 Test

Add to the end of main():

System.out.println("\n--- Parc ---");
Parc parc = new Parc(5);
parc.add(new Voiture(4));
parc.add(new Voiture(6));
parc.add(new Voiture(28));

System.out.println("Size: " + parc.size());  // 3
parc.demarrerTout();
System.out.println(parc.getAt(0));
// Voiture[p=4, demarree=true, v=0.0]
System.out.println(parc);

try {
    parc.getAt(10);
} catch (IllegalArgumentException e) {
    System.out.println("Caught: " + e.getMessage());
}

Part 4 — Exploration (remaining time)

4.1 Add a private static int nbCreees = 0 counter to Voiture, incremented in every constructor. Add public static int getNbCreees(). Test that after creating 5 vehicles the counter returns 5.

4.2 Add a setVitesse(double v) method: only accepts v >= 0 and only works if the car is started. If v < 0, throw IllegalArgumentException.

4.3 Override hashCode() in Voiture:

@Override
public int hashCode() {
    return Integer.hashCode(puissance);
}

Why is it important to override both equals() and hashCode() together? (Hint: think of HashMap<Voiture, String>)

Deliverable

No formal submission for TD1. Verify all outputs match the expected values before leaving.
Keep this project — it will be extended in TD2.

Common Errors

Error	Cause	Fix
`cannot find symbol`	Typo or missing import	Check spelling; `Ctrl+.` in VSCodium to auto-fix
`incompatible types`	Wrong type assigned	Check declared type matches the value
`NullPointerException`	Array slot is `null`	Make sure `count` tracks filled slots correctly
`ArrayIndexOutOfBoundsException`	Index out of range	Guard with `i >= 0 && i < count` in `getAt()`
`accelere()` has no visible effect	Car not started	Call `demarre()` before `accelere()`