04-classes.md

Java Classes

In object-oriented programming, a class serves as a blueprint or a data type from which objects can be created. A class defines the behavior and state of objects instantiated from it.

Example: The "Car" Class

A simple class to represent a car in the Java programming language might look like this:

"Car" Class Implementation

public class Car {
    // Instance variables
    String brand;
    String model;
    int year;

    // Static variable shared among all instances
    static int numberOfCars;

    // Constructor
    public Car(String brand, String model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
        // Incrementing the static variable on each instance creation
        numberOfCars++;
    }

    // Final method that displays information about the car
    public final void displayInfo() {
        System.out.println("Brand: " + brand);
        System.out.println("Model: " + model);
        System.out.println("Year: " + year);
    }

    // Static method to get the total number of cars
    public static int getNumberOfCars() {
        return numberOfCars;
    }
}

Explanation for the "Car" Class Example

In the provided example:

• Car is the name of the class.
• brand, model, and year are instance variables that define the state of objects created from this class.

Keyword static:

• The variable numberOfCars is declared as static, meaning it belongs to the class rather than specific instances. A single copy of this variable is shared among all instances.

Keyword final:

• The method displayInfo is marked with final, indicating that it cannot be overridden in a derived class.

• The variables brand, model, and year are instance variables and are not marked with final. They can be modified after object creation.

Keyword static for methods:

• The method getNumberOfCars is declared as static, allowing it to be called directly on the class without creating an instance. It is useful for operations that don't depend on the specific state of an instance.