Java Object Oriented Programming (OOP) Practice Questions with Solutions

Object-Oriented Programming (OOP) is one of the core concepts of Java. Unlike procedural programming, where programs are divided into functions, OOP organizes programs into objects and classes. This approach makes software easier to develop, maintain, reuse, and scale.

Java is a pure object-oriented programming language (except for primitive data types), and almost every real-world Java application is built using OOP principles.

OOP is widely used in:

• Banking Systems
• E-commerce Applications
• Hospital Management Systems
• Student Management Systems
• Android Applications
• Enterprise Software
• Desktop Applications
• Game Development
• Inventory Management Systems

The four pillars of Object-Oriented Programming are:

• Encapsulation
• Inheritance
• Polymorphism
• Abstraction

Before learning these advanced concepts, you must first understand:

• Classes
• Objects
• Instance Variables
• Instance Methods
• Constructors

In this chapter, you’ll practice beginner-friendly Java OOP programs that build a strong foundation for advanced Java development. Java Object-Oriented Programming (OOP) practice questions with solutions help to understand the concepts.

1. Java Program to Create a Class and Object

Problem Statement

Write a Java program to create a class named Student, create an object of the class, and display a message.

Java Solution

class Student {

    void display() {

        System.out.println("Welcome to Java OOP");

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student();

        student.display();

    }

}

Sample Output

Welcome to Java OOP

Explanation

• A class named Student is created.
• An object named student is created using the new keyword.
• The object’s method is called using the dot (.) operator.

Concepts Covered

• Class
• Object
• Method Calling
• new Keyword

2. Java Program to Store and Display Student Information

Problem Statement

Write a Java program to create a class that stores a student’s name and age, then displays the information.

Java Solution

class Student {

    String name = "Rahul";
    int age = 21;

    void display() {

        System.out.println("Name : " + name);

        System.out.println("Age  : " + age);

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student();

        student.display();

    }

}

Sample Output

Name : Rahul
Age  : 21

Explanation

The class contains two instance variables:

• name
• age

The display() method prints both values.

Concepts Covered

• Class
• Object
• Instance Variables
• Instance Method

3. Java Program to Calculate the Area of a Rectangle Using a Class

Problem Statement

Write a Java program to create a class that calculates the area of a rectangle.

Java Solution

class Rectangle {

    int length = 10;
    int width = 5;

    void area() {

        int result = length * width;

        System.out.println("Area = " + result);

    }

}

public class Main {

    public static void main(String[] args) {

        Rectangle rectangle = new Rectangle();

        rectangle.area();

    }

}

Sample Output

Area = 50

Explanation

The class stores:

• Length
• Width

The area() method calculates:

Area = Length × Width

Concepts Covered

• Class
• Object
• Instance Variables
• Instance Method
• Arithmetic Operations

4. Java Program to Use a Default Constructor

Problem Statement

Write a Java program to create a class with a default constructor that displays a welcome message.

Java Solution

class Student {

    Student() {

        System.out.println("Default Constructor Called");

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student();

    }

}

Sample Output

Default Constructor Called

Explanation

A constructor is a special method that is automatically executed whenever an object is created.

In this program:

• The constructor name is the same as the class name (Student).
• It has no parameters, so it is called a default constructor.
• The constructor is executed automatically when the object is created.

Concepts Covered

• Constructor
• Default Constructor
• Class
• Object Creation

5. Java Program to Use a Parameterized Constructor

Problem Statement

Write a Java program to create a class that uses a parameterized constructor to initialize student details.

Java Solution

class Student {

    String name;
    int age;

    Student(String studentName, int studentAge) {

        name = studentName;
        age = studentAge;

    }

    void display() {

        System.out.println("Name : " + name);

        System.out.println("Age  : " + age);

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student("Rahul", 22);

        student.display();

    }

}

Sample Output

Name : Rahul
Age  : 22

Explanation

Unlike a default constructor, a parameterized constructor accepts values while creating an object.

Student student = new Student("Rahul", 22);

The constructor initializes the instance variables using the provided values.

Concepts Covered

• Parameterized Constructor
• Constructor Parameters
• Instance Variables
• Object Initialization

6. Java Program to Create Multiple Objects of a Class

Problem Statement

Write a Java program to create multiple objects of a class and display their details.

Java Solution

class Student {

    String name;
    int age;

    Student(String name, int age) {

        this.name = name;
        this.age = age;

    }

    void display() {

        System.out.println("Name : " + name);
        System.out.println("Age  : " + age);
        System.out.println();

    }

}

public class Main {

    public static void main(String[] args) {

        Student student1 = new Student("Rahul", 21);
        Student student2 = new Student("Priya", 22);

        student1.display();
        student2.display();

    }

}

Sample Output

Name : Rahul
Age  : 21

Name : Priya
Age  : 22

Explanation

A class can have multiple objects.

Each object maintains its own copy of the instance variables.

Here:

• student1 stores Rahul’s information.
• student2 stores Priya’s information.

Concepts Covered

• Multiple Objects
• Constructors
• Instance Variables
• Object-Oriented Programming

7. Java Program to Display Employee Details Using Objects

Problem Statement

Write a Java program to create an Employee class that stores employee ID, name, and salary, then displays the employee details.

Java Solution

class Employee {

    int id;
    String name;
    double salary;

    Employee(int id, String name, double salary) {

        this.id = id;
        this.name = name;
        this.salary = salary;

    }

    void display() {

        System.out.println("Employee ID : " + id);
        System.out.println("Name        : " + name);
        System.out.println("Salary      : " + salary);

    }

}

public class Main {

    public static void main(String[] args) {

        Employee employee = new Employee(101, "Amit", 55000);

        employee.display();

    }

}

Sample Output

Employee ID : 101
Name        : Amit
Salary      : 55000.0

Explanation

The Employee class stores employee-related information.

The constructor initializes the data, while the display() method prints it.

Concepts Covered

• Classes
• Objects
• Constructors
• Employee Management Example

8. Java Program to Calculate Circle Area Using a Class

Problem Statement

Write a Java program to calculate the area of a circle using a class and object.

Java Solution

class Circle {

    double radius;

    Circle(double radius) {

        this.radius = radius;

    }

    void calculateArea() {

        double area = 3.14159 * radius * radius;

        System.out.println("Area = " + area);

    }

}

public class Main {

    public static void main(String[] args) {

        Circle circle = new Circle(7);

        circle.calculateArea();

    }

}

Sample Output

Area = 153.93791

Explanation

The program stores the radius using the constructor.

The calculateArea() method computes:

Area = π × r × r

Concepts Covered

• Classes
• Objects
• Constructors
• Mathematical Calculations

9. Java Program to Demonstrate the this Keyword

Problem Statement

Write a Java program to demonstrate the use of the this keyword.

Java Solution

class Student {

    String name;

    Student(String name) {

        this.name = name;

    }

    void display() {

        System.out.println("Student Name : " + this.name);

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student("Rohan");

        student.display();

    }

}

Sample Output

Student Name : Rohan

Explanation

The this keyword refers to the current object.

It is commonly used to differentiate between:

• Instance variables
• Constructor parameters

Example:

this.name = name;

Here:

• this.name → Instance variable
• name → Constructor parameter

Concepts Covered

• this Keyword
• Constructors
• Instance Variables

10. Java Program to Create a Bank Account Class

Problem Statement

Write a Java program to create a BankAccount class that stores account holder information and balance.

Java Solution

class BankAccount {

    String accountHolder;
    double balance;

    BankAccount(String accountHolder, double balance) {

        this.accountHolder = accountHolder;
        this.balance = balance;

    }

    void displayAccount() {

        System.out.println("Account Holder : " + accountHolder);
        System.out.println("Balance        : ₹" + balance);

    }

}

public class Main {

    public static void main(String[] args) {

        BankAccount account = new BankAccount("Rahul Sharma", 25000);

        account.displayAccount();

    }

}

Sample Output

Account Holder : Rahul Sharma
Balance        : ₹25000.0

Explanation

The BankAccount class stores:

• Account Holder Name
• Account Balance

The constructor initializes these values, and the displayAccount() method prints the account details.

This is a simple real-world example of object-oriented programming.

Concepts Covered

• Classes
• Objects
• Constructors
• Real-World OOP Example

11. Java Program to Demonstrate Encapsulation

Problem Statement

Write a Java program to demonstrate Encapsulation by making class variables private and accessing them using getter and setter methods.

Java Solution

class Student {

    private String name;

    public void setName(String name) {

        this.name = name;

    }

    public String getName() {

        return name;

    }

}

public class Main {

    public static void main(String[] args) {

        Student student = new Student();

        student.setName("Rahul");

        System.out.println("Student Name : " + student.getName());

    }

}

Sample Output

Student Name : Rahul

Explanation

Encapsulation means hiding data from direct access.

Instead of accessing variables directly, we use:

• Setter Methods → Assign values
• Getter Methods → Retrieve values

This improves security and data integrity.

Concepts Covered

• Encapsulation
• Private Variables
• Getter Methods
• Setter Methods

12. Java Program to Create a Simple Car Class

Problem Statement

Write a Java program to create a Car class that stores the brand, model, and manufacturing year.

Java Solution

class Car {

    String brand;
    String model;
    int year;

    Car(String brand, String model, int year) {

        this.brand = brand;
        this.model = model;
        this.year = year;

    }

    void display() {

        System.out.println("Brand : " + brand);
        System.out.println("Model : " + model);
        System.out.println("Year  : " + year);

    }

}

public class Main {

    public static void main(String[] args) {

        Car car = new Car("Toyota", "Fortuner", 2024);

        car.display();

    }

}

Sample Output

Brand : Toyota
Model : Fortuner
Year  : 2024

Explanation

The Car class represents a real-world object.

Each car object has its own:

• Brand
• Model
• Year

Concepts Covered

• Classes
• Objects
• Constructors
• Real-World OOP Example

13. Java Program to Create a Book Class

Problem Statement

Write a Java program to create a Book class that stores the title, author, and price.

Java Solution

class Book {

    String title;
    String author;
    double price;

    Book(String title, String author, double price) {

        this.title = title;
        this.author = author;
        this.price = price;

    }

    void display() {

        System.out.println("Title  : " + title);
        System.out.println("Author : " + author);
        System.out.println("Price  : ₹" + price);

    }

}

public class Main {

    public static void main(String[] args) {

        Book book = new Book("Java Programming", "James Gosling", 699);

        book.display();

    }

}

Sample Output

Title  : Java Programming
Author : James Gosling
Price  : ₹699.0

Explanation

This program demonstrates how objects can represent books with different properties.

Each object stores its own values.

Concepts Covered

• Objects
• Constructors
• Classes
• Instance Variables

14. Java Program to Create a Product Class

Problem Statement

Write a Java program to create a Product class that stores product details.

Java Solution

class Product {

    int productId;
    String productName;
    double price;

    Product(int productId, String productName, double price) {

        this.productId = productId;
        this.productName = productName;
        this.price = price;

    }

    void display() {

        System.out.println("Product ID   : " + productId);
        System.out.println("Product Name : " + productName);
        System.out.println("Price        : ₹" + price);

    }

}

public class Main {

    public static void main(String[] args) {

        Product product = new Product(101, "Laptop", 65000);

        product.display();

    }

}

Sample Output

Product ID   : 101
Product Name : Laptop
Price        : ₹65000.0

Explanation

The Product class represents products available in an inventory system.

Each object stores different product details.

Concepts Covered

• Classes
• Objects
• Constructors
• Inventory Example

15. Java Program to Create a Mobile Class

Problem Statement

Write a Java program to create a Mobile class that stores the mobile brand, model, and price.

Java Solution

class Mobile {

    String brand;
    String model;
    double price;

    Mobile(String brand, String model, double price) {

        this.brand = brand;
        this.model = model;
        this.price = price;

    }

    void display() {

        System.out.println("Brand : " + brand);
        System.out.println("Model : " + model);
        System.out.println("Price : ₹" + price);

    }

}

public class Main {

    public static void main(String[] args) {

        Mobile mobile = new Mobile("Samsung", "Galaxy S25", 79999);

        mobile.display();

    }

}

Sample Output

Brand : Samsung
Model : Galaxy S25
Price : ₹79999.0

Explanation

The Mobile class is another real-world OOP example.

It stores information related to a smartphone and displays it using an object method.

Concepts Covered

• Classes
• Objects
• Constructors
• Real-World OOP Model

Chapter Summary

In this chapter, you learned the fundamentals of Object-Oriented Programming (OOP) in Java. OOP is the backbone of Java development and is used to build scalable, reusable, and maintainable software.

You practiced creating and using:

• Classes
• Objects
• Instance Variables
• Instance Methods
• Default Constructors
• Parameterized Constructors
• Multiple Objects
• Real-world classes such as Student, Employee, Bank Account, Product, Book, Car, and Mobile
• Encapsulation using Getter and Setter methods
• The this keyword for object initialization

These concepts form the foundation for advanced Java topics such as Inheritance, Polymorphism, Abstraction, Interfaces, Packages, Exception Handling, Collections Framework, and Spring Boot Development.

Understanding OOP is essential for Java interviews and professional software development because almost every Java application is designed using object-oriented principles.

Key Takeaways

• A class is a blueprint for creating objects.
• An object is an instance of a class.
• Constructors initialize objects automatically during creation.
• Java provides:
  • Default Constructors
  • Parameterized Constructors
• The this keyword refers to the current object.
• Encapsulation protects data using private variables and getter/setter methods.
• Objects can represent real-world entities such as students, employees, products, and bank accounts.
• OOP improves code reusability, modularity, and maintainability.
• Java is primarily an object-oriented programming language.
• Strong OOP knowledge is essential before learning inheritance and polymorphism.

Frequently Asked Questions (FAQs)

1. What is Object-Oriented Programming (OOP)?

Object-Oriented Programming (OOP) is a programming paradigm that organizes software into classes and objects, making code modular, reusable, and easier to maintain.

2. What is the difference between a class and an object?

Example:

Student student = new Student();

Here:

• Student → Class
• student → Object

3. What is a constructor in Java?

A constructor is a special method that is automatically executed whenever an object is created.

Example:

Student() {

    System.out.println("Constructor Called");

}

4. What is the purpose of the this keyword?

The this keyword refers to the current object.

Example:

this.name = name;

It differentiates the instance variable from the constructor parameter.

5. What is Encapsulation?

Encapsulation is the process of hiding data using private variables and providing controlled access through getter and setter methods.

Example:

private String name;

6. What are the four pillars of OOP?

The four pillars of Object-Oriented Programming are:

• Encapsulation
• Inheritance
• Polymorphism
• Abstraction

7. Why is OOP important in Java?

OOP helps developers build:

• Reusable Code
• Modular Applications
• Secure Programs
• Scalable Software
• Maintainable Systems

It is the foundation of almost every Java application.

8. Where is OOP used in real-world applications?

Object-Oriented Programming is used in:

• Banking Software
• E-commerce Applications
• Android Apps
• Desktop Applications
• Hospital Management Systems
• Student Management Systems
• Inventory Systems
• Enterprise Applications
• Game Development
• Web Applications

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar