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Classes and Objects in Java

Classes and Objects in Java

In Java, classes and objects are the building blocks of object-oriented programming (OOP). They provide a way to structure code, organize data, and encapsulate behavior. This article explores the concepts of classes and objects in Java, along with practical examples to illustrate their usage.

1. Classes in Java:

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

// Example of a simple class
public class Car {
// Attributes
String make;
String model;
int year;

// Method
public void startEngine() {
System.out.println(“Engine started.”);


  • The Car class has attributes (make, model, year) and a method (startEngine).
  • Attributes represent the state of an object, and methods define its behavior.

2. Objects in Java:

An object is an instance of a class. It represents a real-world entity and encapsulates the data and behavior defined by its class.

public class CarDemo {
public static void main(String[] args) {
// Creating objects of the Car class
Car myCar = new Car();
Car friendCar = new Car();

// Accessing and modifying object attributes
myCar.make = “Toyota”;
myCar.model = “Camry”;
myCar.year = 2022;

// Calling object methods

// Accessing attributes of another object
friendCar.make = “Honda”;
friendCar.model = “Civic”;
friendCar.year = 2021;


  • Objects (myCar and friendCar) are created using the new keyword and the class constructor.
  • Object attributes are accessed using the dot notation (objectName.attribute).
  • Object methods are called using the dot notation (objectName.method()).

3. Constructors:

A constructor is a special method that is called when an object is created. It initializes the object’s state.

public class Book {
String title;
String author;

// Constructor
public Book(String title, String author) {
this.title = title; = author;


  • The Book class has a parameterized constructor that initializes the title and author attributes.
  • The this keyword refers to the current object.

4. Encapsulation:

Encapsulation is the principle of bundling data (attributes) and methods that operate on the data within a single unit (class).

public class Student {
private String name;
private int age;

// Getter and setter methods for encapsulation
public String getName() {
return name;

public void setName(String name) { = name;

public int getAge() {
return age;

public void setAge(int age) {
if (age > 0) {
this.age = age;


  • The private keyword restricts direct access to the name and age attributes.
  • Getter and setter methods provide controlled access to the attributes.

5. Inheritance:

Inheritance is a mechanism in OOP that allows a class to inherit properties and behaviors from another class.

public class Animal {
void eat() {
System.out.println(“Animal is eating.”);

public class Dog extends Animal {
void bark() {
System.out.println(“Dog is barking.”);


  • The Dog class extends the Animal class, inheriting the eat method.
  • The Dog class introduces a new method, bark.

6. Key Concepts:

a. Polymorphism:

  • Polymorphism allows objects of different classes to be treated as objects of a common superclass.

b. Abstraction:

  • Abstraction involves hiding the complex implementation details and showing only the necessary features of an object.

7. Conclusion:

Classes and objects form the backbone of Java’s object-oriented paradigm. They provide a structured and modular way to design and organize code. By understanding and leveraging the concepts of classes, objects, constructors, encapsulation, inheritance, and more, Java developers can create scalable, maintainable, and extensible software applications.

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