Java Basics: Building a Car Class from Scratch

Day 38 of the AI foundational learning series emphasizes that persistence is hard to maintain, then presents a concrete Java example: a Car class.

The class defines four instance variables— brand, color, speed, and id —and a static class variable count used to track how many Car objects have been created. A parameterized constructor initializes the instance fields and increments count, assigning the new value to id so each object receives a unique identifier.

public class Car{
    // car brand
    private String brand;
    // car color
    private String color;
    // car speed
    private double speed;
    // object identifier
    private int id;
    // static counter for all Car instances
    private static int count = 0;

    // constructor with parameters
    public Car(String brand, float color, int speed){
        this.brand = brand;
        this.color = color;
        this.speed = speed;
        // increment counter and assign to id
        id = ++count;
    }

    // get id
    public int getId(){
        return id;
    }

    // get total number of Car objects
    public static int getCount(){
        return count;
    }

    // get brand
    public String getBrand(){
        return brand;
    }

    // get color
    public String getColor(){
        return color;
    }

    // get speed
    public double getSpeed(){
        return speed;
    }

    // set speed
    public void setSpeed(int newSpeed){
        speed = newSpeed;
    }
}

The accompanying diagram (shown below) visualizes the relationship between the instance variables and the static counter.

Each time the constructor runs, count increases by one, providing a simple way to track object creation and assign a sequential identifier to each Car instance. This example demonstrates fundamental object‑oriented programming concepts such as encapsulation, static members, and constructor logic in Java.