Classes and Objects

Table of Contents

• Introduction
• Class
• Object
• Access Modifiers
• References

Introduction

OOPS stands for Object Oriented Programming System. It is a programming paradigm that uses classes and objects to represent real-world entities and their interactions.Classes and objects form the foundation of OOPs.

Class

A class is blueprint or template for creating objects. It defines a set of attributes(fields) and behaviors(methods) of an object.

To define a class, we use the class keyword.

Examples

Java

public class Car{
    // Attributes
    private String brand;
    private String model;
    private int year;

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

    // Methods
    public void displayInfo(){
        System.out.println("Brand: " + brand + ", Model: " + model +
                           ", Year: " + year);
    }
}

Output

Brand: Toyota, Model: Corolla, Year: 2020
Brand: Ford, Model: Mustang, Year: 2021

• Attributes : The class Car has three attributes that describes its state: brand, model, and year.
• Constructor : The constructor is a special method that initializes the object. It is called when an object is created using the new keyword.
• Methods : The class Car has one method that displays the car's information.

Object

An object is an instance of a class. When you create an object, you are bringing the blueprint of the class into reality. It consists of state and behavior defined by the class, with each object holding its own copy of the data.

To create an object, we use the new keyword followed by class constructor.

Examples

Java

public class Main{
    public static void main(String... args){
        Car toyota = new Car("Toyota", "Corolla", 2020);
        Car ford = new Car("Ford", "Mustang", 2021);
        toyota.displayInfo();
        ford.displayInfo();
    }
}

Output

Brand: Toyota, Model: Corolla, Year: 2020
Brand: Ford, Model: Mustang, Year: 2021

• Instantiation : The new keyword is used to create an object, which allocates memory to the object.
• Initialization : The constructor Car is used to initialize the object.
• Reference : The toyota and ford are references to the objects.

Access Modifiers

Access modifiers are used to restrict the access of the class members.

Java

public class Car{
    public String brand;
    private String model;
    public int price;
    protected int year;
}

References

• GeeksforGeeks