The object as an instance of a class

This lesson was translated automatically – it may contain errors.

What is an object (or an instance)?

Back to our car blueprint. If the class is the blueprint, then an object (or an instance) is a particular car built from it.

You can build several different cars from one and the same blueprint: one a red racing car, another a blue truck. In the same way, many objects can be created from a single class.

An object is a concrete entity in the computer’s memory, created from the description a class gives. It has concrete values for its attributes and can perform methods.

Creating objects (instances) of the Car class

namespace Lecture1;

class Program
{
    static void Main(string[] args)
    {
        // Creating two objects (instances) of the Car class
        var myCar = new Car("red", "Tesla Model S");
        var yourCar = new Car("blue", "Toyota Camry");

        // Every object has attribute values of its own
        Console.WriteLine(myCar.Color); // Prints: red
        Console.WriteLine(yourCar.Model); // Prints: Toyota Camry

        // And can perform methods
        myCar.StartEngine(); // Prints: Engine started!
        yourCar.Drive(); // Prints: Start the engine first!
    }
}

int main() {
    // Creating two objects (instances) of the Car class – right on the stack
    Car my_car("red", "Tesla Model S");
    Car your_car("blue", "Toyota Camry");

    // Every object has attribute values of its own
    std::cout << my_car.color() << std::endl;   // Prints: red
    std::cout << your_car.model() << std::endl; // Prints: Toyota Camry

    // And can perform methods
    my_car.StartEngine(); // Prints: Engine started!
    your_car.Drive();     // Prints: Start the engine first!

    return 0;
}

func main() {
	// Creating two objects (instances) of the Car type
	myCar := NewCar("red", "Tesla Model S")
	yourCar := NewCar("blue", "Toyota Camry")

	// Every object has field values of its own
	fmt.Println(myCar.Color)   // Prints: red
	fmt.Println(yourCar.Model) // Prints: Toyota Camry

	// And can perform methods
	myCar.StartEngine() // Prints: Engine started!
	yourCar.Drive()     // Prints: Start the engine first!
}

# Creating two objects (instances) of the Car class
my_car = Car("red", "Tesla Model S")
your_car = Car("blue", "Toyota Camry")

# Every object has attribute values of its own
print(my_car.color)   # Prints: red
print(your_car.model) # Prints: Toyota Camry

# And can perform methods
my_car.start_engine() # Prints: Engine started!
your_car.drive()      # Prints: Start the engine first!

// Creating two objects (instances) of the Car class
const myCar = new Car("red", "Tesla Model S");
const yourCar = new Car("blue", "Toyota Camry");

// Every object has attribute values of its own
console.log(myCar.color);   // Prints: red
console.log(yourCar.model); // Prints: Toyota Camry

// And can perform methods
myCar.startEngine(); // Prints: Engine started!
yourCar.drive();     // Prints: Start the engine first!

public class Program {
    public static void main(String[] args) {
        // Creating two objects (instances) of the Car class
        Car myCar = new Car("red", "Tesla Model S");
        Car yourCar = new Car("blue", "Toyota Camry");

        // Every object has attribute values of its own
        System.out.println(myCar.getColor());   // Prints: red
        System.out.println(yourCar.getModel()); // Prints: Toyota Camry

        // And can perform methods
        myCar.startEngine(); // Prints: Engine started!
        yourCar.drive();     // Prints: Start the engine first!
    }
}

fun main() {
    // Creating two objects (instances) of the Car class
    val myCar = Car("red", "Tesla Model S")
    val yourCar = Car("blue", "Toyota Camry")

    // Every object has attribute values of its own
    println(myCar.color)   // Prints: red
    println(yourCar.model) // Prints: Toyota Camry

    // And can perform methods
    myCar.startEngine() // Prints: Engine started!
    yourCar.drive()     // Prints: Start the engine first!
}

The main difference between a class and an object

A simple analogy: the class CookieCutter is a cookie cutter. The objects cookie1, cookie2 are the cookies themselves, made with that cutter.

In summary: a class is the general idea, an object is its material embodiment. Understanding that difference is the key to object-oriented programming. You write classes to describe the entities of your world, and you create objects of those classes to work with them in your program.