Fullstack Masters

Java Essentials: Master the Basic Concepts of OOPs in Java Programming

Basic Concepts of OOPs in Java

Java is one of the most latest programming languages in the world. It is an essential tool for developers, partly due to its compatibility across different platforms. But, more importantly, Java is object-oriented. That means it can handle complexity in software design, making it an ideal choice for developers. By mastering the basic concepts of object-oriented programming in Java, developers can write more robust, maintainable, and scalable code.

This article will delve into the fundamental concepts of object-oriented programming in Java. We will explore using classes and objects, encapsulation, inheritance, polymorphism, abstraction, and interfaces. Additionally, we will examine various perspectives and approaches to OOPs in Java.

Basic Concepts of OOPs in Java

Object-Oriented Programming

Object-Oriented Programming (OOP) is a reaction to programming based on the concept of objects (class instances). It depends on the construction of software on real-world elements and concepts.

In OOP, objects are created from classes, which define the attributes and behaviour of those objects. Attributes are characteristics of an object, such as its colour or size, while behaviour is what an object can do or how it can interact with other objects.

Encapsulation is a critical concept in OOP, which means that data is protected from outside access and can only be modified through defined methods. That improves data protection and makes it easier to change the behaviour of an object or class without breaking other parts of the program.

Another vital OOP concept is inheritance, which allows new classes to inherit traits and methods from existing ones. These promote code reuse and make the design process more straightforward.

Polymorphism is also a fundamental concept of OOP, which allow objects of different types to be treated as objects of a common superclass. That enables dynamic method dispatch and makes it easier to write modular code.

Java is an object-oriented language.

Java is widely recognized as an object-oriented programming language. That means that the language is designed around the concept of objects, which are significant classes. Everything is treated as an object in Java, from simple data types to complex data structures.

Being object-oriented allows Java to provide several key features that make it a powerful and flexible language. One required benefit of object-oriented programming is encapsulation, which allows the state and behaviour of objects to be controlled and protected. That promotes code reusability, modularity, and maintainability.

Another important feature of Java’s object-oriented nature is inheritance. Inheritance allows new classes to inherit properties and methods from existing classes, promoting code reuse and allowing for hierarchical organization of classes. That promotes code extensibility and simplifies the design and implementation process.

Additionally, Java supports polymorphism, which allows objects of different kinds to be treated as objects of a common superclass. That enables dynamic method dispatch and allows for more flexible and modular code.

Classes and Objects

Classes are the heart of object-oriented programming. They represent a blueprint or prototype of an object. It defines the properties and functionality that instance objects of that class inherit. An object is an instance of a class.

Creating objects is easy in Java. You first define a class and then create objects based on that class. 

Here’s an example:

public Class Person { private String name; private int age; public void setName(String name) { this.name = name; } public String getName() { return this.name; } public void setAge(int age) { this.age = age; } public int getAge() { return this.age; }}Person person = new Person();person.setName(“John Doe”);person.setAge(25);


Encapsulation is one of the fundamental concepts of object-oriented programming (OOP). It is a principle that promotes the bundling of data (attributes) and methods (behaviors) together within a class. Encapsulation hides the internal details of an object and provides a controlled interface to interact with it.


In encapsulation, the internal state of an object is kept private and can only be accessed or modified through public methods, also known as accessors and mutators. This ensures that the integrity and consistency of the object’s data are maintained.


Data hiding: The attributes of an object are generally declared as private, restricting direct access from outside the class. This means that other objects cannot modify the internal state of an object directly. Instead, access to the object’s data is provided through public methods.


Accessors (Getters): These methods are used to retrieve the values of private attributes. They provide read-only access to the object’s data.


Mutators (Setters): These methods are used to modify the values of private attributes. They provide a controlled way to update the object’s data while maintaining any necessary validations or conditions.


Information hiding: Encapsulation allows the internal implementation details of an object to be hidden. This means that the object’s interface (public methods) can remain constant, even if the internal implementation changes. This helps to decouple different parts of the codebase and allows for easier maintenance and modifications.


Data validation and control: Encapsulation allows validation logic to be placed within the object’s mutators. This way, before modifying the internal state of an object, the mutator methods can perform checks and ensure that the data is valid and consistent.


Encapsulation is a key principle in OOP as it helps to achieve data protection, code organization, modularity, and reusability. By encapsulating data and related behavior within a class, the complexity of the code can be managed, and changes can be made more easily without affecting other parts of the program.


Inheritance is a mechanism provided by object-oriented programming that allows for classes to inherit properties and behaviour from other classes called superclasses. This mechanism promotes code reusability and is used extensively in Java.

In Java, inheritance is created using the “extends” keyword. When an object is instantiated from a subclass, its constructors run automatically. Access to inherited members is done using the accessor methods provided in the superclass or the protected keyword.

public class Shape { protected double area; public void setArea(double area) { this.area = area; } public double getArea() { return area; }}public class Square extends Shape { private double length; public Square(double length) { this.length = length; calculate area(); } private void calculate area() { area = length * length; }}Square square = new Square(5.0);square.getArea(); // returns 25.0


Polymorphism is the idea of one object taking on different forms. It is made possible by inheritance and abstraction. In Java, polymorphism is achieved through method overriding and method overloading.

Method overriding involves a subclass providing a different implementation of a method in its superclass. That enables objects to take on different forms at runtime. When a method is overridden in a subclass, the superclass’s version of the method is hidden.

Method overloading, on the other hand, involves a subclass defining a new method with the same name as a method that is present in its superclass. Overridden methods have the same name and parameter lists, whereas overloaded methods differ in parameter lists.

Public void makeSound() public class Animal System.out.println(“Animal is making a sound”); public class Animal extends by a dog @Override public void makeSystem.out.println(“Dog is barking”); 

public void makeSound(int count) 

for(int i = 0; i count; i++) System.out.println(“Bark!”); // prints “Dog is barking.” Animal dog = new Dog (); Dog.make sound(); // prints “Dog is barking.”


Abstraction simplifies complex systems and concepts by breaking them down into smaller, more manageable components. In object-oriented programming, abstraction is used to create models of real-world objects. Objects must expose only the data and behaviour necessary to achieve their purpose.


In Java, abstraction is implemented using abstract classes and interfaces. An abstract class is a class that cannot be instantiated. Instead, subclasses extend the abstract class and provide their implementation of its abstract methods.


An interface is a set of abstract techniques. It defines a blueprint that classes implement. By defining methods in an interface, Java provides a way to apply expected behaviour to unrelated classes.


public abstract class Animal { protected String name; public abstract void makeSound(); public void setName(String name) { this.name = name; } public String getName() { return this.name; }}public class Dog extends Animal { @Override public void makeSound() { System.out.println(“Dog is barking”); }}Animal dog = new Dog();dog.setName(“Rex”);dog.make sound(); // prints “Dog is barking.”


An interface is a set of abstract techniques. Defining a set of class capabilities. In Java, interfaces are used to create contracts between unrelated classes.


An interface is similar to a class but cannot be instantiated. Classes implement interfaces, which means they agree to provide implementations of all of the interface’s methods.


public interface Drawable { void draw();}public class Circle implements Drawable { public void draw() { // draw a circle }}public class Rectangle implements Drawable { public void draw() { // draw a rectangle }}Circle circle = new Circle();circle.draw(); // draws a circle

Principles of Object-Oriented Design

Principles of Object-Oriented Design refer to a set of guidelines and best practices that help developers design and structure their software using the principles of object-oriented programming. These principles aim to improve the software’s modularity, reusability, maintainability, and scalability. One commonly recognized set of principles is the SOLID principle. These principles, coined by Robert C. Martin (also known as Uncle Bob), are as follows:

  1. Single Responsibility Principle (SRP): A class should have only one reason to change and one responsibility. This principle promotes high cohesion and reduces the likelihood of code duplication or excessive coupling.
  2. Open/Closed Principle (OCP): Software entities (classes, modules, functions, etc.) should be accessible but not adaptable. This strategy encourages the application of abstractions and interfaces that allow for incorporating new functionality without altering current code.
  3. Liskov Substitution Principle (LSP): Objects of a superclass should be replaceable with objects of its subclasses without affecting the correctness of the program. This principle ensures that subtypes adhere to the contract defined by their supertypes.
  4. Interface Segregation Principle (ISP): Clients should not be forced to depend on interfaces they’re comfortable with. This notion encourages the development of client-specific interfaces, hence reducing the cost of developing unneeded methods.
  5. Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules; both should depend on abstractions. This principle encourages loose coupling between modules by depending on interfaces or abstract classes rather than concrete implementations.

Implementing the SOLID principles in object-oriented design helps to create more maintainable, flexible, and extensible software systems. By adhering to these principles, developers can design modular and loosely coupled systems that are easier to understand, test, and modify.

Other object-oriented design principles include the DRY principle (Don’t Repeat Yourself), which promotes the elimination of code duplication, and the GRASP principles (General Responsibility Assignment Software Principles), which provide guidelines for assigning responsibilities to different classes or objects in a system.

Object-oriented design principles, such as the SOLID principles, provide guidelines for designing modular, maintainable, and scalable software systems. Adhering to these principles can lead to more robust and flexible codebases.

Applications of oop in Java

Object-Oriented Programming (OOP) has various applications in Java. Some of the standard applications include:

  1. Software Design and Development: OOP enables developers to design and develop modular, flexible, and scalable software systems. It provides a way to model real-world entities as objects, allowing for a better understanding and organization of code structure.
  2. Code Reusability: OOP promotes code reusability through features like inheritance and polymorphism. Inheritance allows the creation of classes that inherit properties and methods from existing classes, enabling code reuse. Polymorphism allows using a single interface and multiple implementations, making reusing and extending code without modification easier.
  3. Graphical User Interface (GUI) Development: OOP is widely used in developing GUI applications in Java. It allows developers to create GUI components as objects with their properties and behaviours. That simplifies the development process by providing a modular and reusable approach to building user interfaces.
  4. Database Programming: OOP concepts are used in Java database programming to create objects that model tables and perform database operations. OOP provides an intuitive way to represent database entities, relationships, and actions as objects, making database programming more organized and maintainable.
  5. Game Development: OOP is extensively used in Java game development. It allows developers to represent game elements such as characters, items, and environments as objects. OOP’s encapsulation, inheritance, and polymorphism features enable the creation of reusable and modular game components, facilitating the development and maintenance of complex game systems.
  6. Enterprise Application Development: OOP creates objects that model various business entities and processes in enterprise applications. OOP enables the design and implementation of modular and scalable enterprise systems, providing flexibility in adapting to changing business requirements.

The principles of OOP help improve code organization, reusability, and maintainability, making it a widely used programming paradigm for various applications.

What is single inheritance in Java

Single inheritance in Java refers to the concept where a Java class can only inherit from one parent class. In other words, a child class can have only one direct superclass. That means that a class can extend another class, inheriting its properties and methods but cannot simultaneously extend multiple classes.


For example, consider a class hierarchy where class B extends class A. Here, class B is the child class and class A is the parent class. B can inherit all A’s members (variables and methods), but it cannot directly inherit from any other class. This restriction on single inheritance ensures simplicity and avoids complications from multiple inheritance.


The syntax for single inheritance in Java is straightforward. To create a child class that inherits from a parent class, the extends keyword is used to define the relationship.

Here’s an example:

class A {

   // parent class members


class B extends A {

   // child class members


In the above example, class B extends class A, making class A the superclass and class B the subclass. As a result, class B will inherit all the properties and behaviours of class A.

It’s important to note that even though a Java class can have only one direct superclass, it can still indirectly inherit multiple classes through a hierarchy of inheritance. This hierarchical inheritance structure allows for a flexible and organized approach to building class relationships in Java.

Single inheritance in the Java example program

class Vehicle { void engineStart() { System.out.println(“Vehicle Engine Started”); }}class Car extends Vehicle { void accelerate() { System.out.println(“Car Accelerating”); }}public class Main { public static void main(String[] args) { Car myCar = new Car(); myCar.engineStart(); myCar.accelerate(); }}

In this example, we have a superclass called Vehicle with a method engineStart() that prints “Vehicle Engine Started”. The Car class extends the Vehicle class using the extends keyword. It has an additional method, accelerate(), that prints “Car Accelerating”. In the primary method, we create an object of the Car class and call the engine start () and accelerate() methods.

This program demonstrates the concept of single inheritance, where the Car class inherits the properties and methods of the Vehicle class.

Diverse Perspectives

Object-oriented programming has evolved significantly since its inception. Different programming paradigms, languages, and communities have influenced it. Java is just one way of practising OOP.

From functional programming in C# and Python to procedural programming in C and Perl, several software development approaches exist. Learning diverse perspectives and approaches to improve skills and stay current in the constantly evolving world of software development is essential.


When used correctly, Java is a potent programming language that can help writers create more robust and maintainable code. Developers can create cleaner, more flexible, and adaptable code by mastering the foundational concepts of OOPs in Java programming, including classes and objects, encapsulation, inheritance, polymorphism, abstraction, and interfaces.

Furthermore, by understanding diverse perspectives and practices across multiple programming languages and paradigms, developers can expand their grasp of OOP and stay competitive in a rapidly evolving field.

Frequently asked questions about the basic concepts of Object-Oriented Programming in Java: