Class and Object in Java

Class

A class in Java is a blueprint or template for creating objects. It defines the properties (attributes) and behaviors (methods) that all objects of the class will have.

                    
// Class declaration
public class Car {
    // Instance variables (attributes)
    private String brand;
    private String model;
    private int year;

    // Constructor (used to initialize objects)
    public Car(String brand, String model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
    }

    // Method to display car details
    public void displayDetails() {
        System.out.println("Brand: " + brand);
        System.out.println("Model: " + model);
        System.out.println("Year: " + year);
    }

    // Getter and setter methods for encapsulation
    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }
}

In this example:

Class Name: Car
Attributes: brand, model, and year are instance variables (also called fields).
Constructor: Car(String brand, String model, int year) initializes the object with the provided values for brand, model, and year.
Methods: displayDetails(): Prints the details of the car (brand, model, year).
Getter and setter methods: Used for encapsulation to control access to the class fields (getBrand(), setBrand(), etc.).

Object

An object is an instance of a class. It represents a specific entity with its own state (attributes) and behavior (methods), based on the blueprint defined by its class.

                    
// Using the Car class

public class Main {
    public static void main(String[] args) {
        // Creating instances (objects) of the Car class
        Car car1 = new Car("Toyota", "Camry", 2023);
        Car car2 = new Car("Honda", "Accord", 2022);
        
        // Accessing methods and properties of objects
        car1.displayDetails();  // Output: Brand: Toyota, Model: Camry, Year: 2023
        car2.displayDetails();  // Output: Brand: Honda, Model: Accord, Year: 2022
        
        // Using getter and setter methods
        car1.setYear(2024);  // Update the year of car1
        System.out.println("Updated Year of Car 1: " + car1.getYear());  // Output: Updated Year of Car 1: 2024
    }
}

In this Main class:

Object Creation: Car car1 = new Car("Toyota", "Camry", 2023); and Car car2 = new Car("Honda", "Accord", 2022); create two instances (objects) of the Car class.
Accessing Methods: car1.displayDetails() and car2.displayDetails() call the displayDetails() method on each object to print their respective details.
Using Setter and Getter: car1.setYear(2024) updates the year attribute of car1, and car1.getYear() retrieves the updated value.