Abstraction in Java: Concepts, Examples, and Usage

Shailendra Chauhan  19 min read
22 Sep 2023

Abstraction in Java: An Overview

Java Abstraction is an essential concept in the world of computer programming and is crucial for anyone looking to learn Java.  The ability to use abstractions in Java can be a great benefit in the context of Java Online Training because it allows you to separate out different layers of complexity and work with them independently. In this article, we'll take a look at how Java abstraction works, what its advantages are, and abstraction in Java, abstraction program in Java, Java abstraction example, abstract method in Java example, and some tips for getting started with implementing abstractions into your own codebase.

Abstraction in Java

  • Abstraction in Java is a powerful concept that enables developers to create complex applications without having to worry about low-level details such as data type and variable in Java, memory management, and platform independence.
  • It’s achieved by simplifying complex code, hiding details of how things work, and providing developers with the ability to handle detailed operations without losing track of the bigger picture.
  • Through the use of concepts like abstract classes, methods, interfaces, superclasses, and polymorphism, abstraction in Java streamlines development by hiding complicated features.
  • It enables developers to concentrate on the crucial elements, making code upkeep and feature additions simpler.

Example of abstraction program in Java

public abstract class Animal {
  private String name;
  public Animal(String name) {
    this.name = name;
  public abstract void makeSound();
public class Dog extends Animal {
  public Dog(String name) {
  public void makeSound() {
public class Main {
  public static void main(String[] args) {
    Animal myDog = new Dog("Fido");

The abstract class "Animal" in this Java code has the method "makeSound," whereas the concrete subclass "Dog" overrides "makeSound" to print "Woof!" when a "Dog" object is created and called in the "main" method.



Ways to achieve Abstraction in Java

  • Programming in Java requires abstraction.
  • In order to construct universal methods that are shared by related objects, abstract classes—which cannot be instantiated—are used.
  • Different classes of behavior protocols are defined via interfaces.
  • By separating classes from one another, inner classes provide abstraction.
  • From other code segments, packages conceal the specifics of items.
  • Java programming can achieve effective abstraction by using these methods.

When to use Abstract classes and abstract method

  • Superclasses don't have to implement every method to define the structure of an abstraction.
  • Superclasses can offer a generalization that all subclasses share, enabling each subclass to offer particular specifics.
  • Shapes are used as an example, where the base type "shape" is defined with typical characteristics like color and size.
  • Particular forms like circles, squares, and triangles derive from the basic class "shape".
  • Subclasses might include extra traits and actions like flipping for specific shapes.
  • Subclasses can manage behavioral variations like calculating area.
  • The type hierarchy identifies the differences and similarities among shapes.

Abstract Class in Java

  • An abstract class in Java serves as a blueprint for other classes so that they can share abstractions and implementations.
  • It is the superclass that contains mixtures of abstract methods, which have to be overridden by subclasses, and concrete methods, which can be used without modification.
  • By creating abstract classes and abstract methods, Java allows developers to enforce a design pattern that must be implemented at the subclass level.
  • Abstract classes provide a foundation for better code structure by providing abstract methods to act as building blocks for more specific functionality.
  • Ultimately, abstract classes can help developers develop well-structured programs and reduce repetitive coding.


abstract class Shape {
    int numSides;
    public Shape(int numSides) {
        this.numSides = numSides;
    public abstract double getArea();
class Rectangle extends Shape {
    int length, width;
    public Rectangle(int length, int width) {
        this.length = length;
        this.width = width;
    public double getArea() {
        return length * width;
public class Main {
    public static void main(String[] args) {
        Shape rect = new Rectangle(5, 10);
        System.out.println("Number of sides: " + rect.numSides);
        System.out.println("Area of rectangle: " + rect.getArea());

This example creates an abstract class called "Shape" with the fields "numSides" and "getArea()." A "Rectangle" class is then added to it, which determines a rectangle's area. A rectangle object is created in the "Main" class, and its area and number of sides are printed.


Number of sides: 4
Area of rectangle: 50.0

Abstract Method in Java

  • Abstract methods in Java are a type of method declaration that lacks an implementation.
  • They are a fundamental concept in Object-Oriented Programming.
  • Abstract methods cannot be implemented within their class, and other classes must extend the parent abstract class and provide their own implementation for the abstract method.
  • Abstract methods serve a useful purpose when the desired behavior of the method should remain consistent while allowing different implementations within different classes.
  • They are commonly used when dealing with polymorphism and inheritance, helping to reduce code duplication and simplify code structure.
  • Abstract methods help keep code easier to maintain by designating differences between different objects whilst keeping related behaviors similar.


public class Rectangle extends Shape {
   private double length;
   private double width;
   public Rectangle(double length, double width) {
      this.length = length;
      this.width = width;
   public double getArea() {
      return length * width;

The "Rectangle" class in this example is an inheritor of the "Shape" class. When the "getArea()" method is used, it computes and returns the area of a rectangle depending on its length and width.


Area of rectangle: 50.0

Interface in Java

  • Interface in Java can be an incredibly useful tool for creating robust and extensible software.
  • A Java Interface allows developers to define a set of related methods that must be implemented by classes that implement the Interface, providing access to the same types of data regardless of the concrete implementation.
  • This helps enforce coding standards and conventions while allowing developers maximum flexibility in implementing parts of a program.
  • Interfaces are also used to increase modularity, improving scalability, reuse, and significant reductions in development time.
  • Interface usage is ubiquitous within server-side application development with frameworks such as Spring providing an Interface-based approach to developing applications.

Example of interface program in Java

// Define the interface
interface Animal {
    public void makeSound();
// Define a class that implements the interface
class Cat implements Animal {
    public void makeSound() {
// Define another class that implements the interface
class Dog implements Animal {
    public void makeSound() {
// Test the interface and the classes that implement it
public class InterfaceExample {
    public static void main(String[] args) {
        Animal myCat = new Cat();
        Animal myDog = new Dog();

This example shows how to use the "Animal" interface and its two implementing classes, "Cat" and "Dog." It enables the "makeSound()" method, which prints out the corresponding noises "Meow" and "Woof" when called in the "main" method, to be called by objects of these types.



Why do we use abstract class?

  • Java's abstract keyword is used to create abstract classes.
  • Java restricts the creation and use of abstract classes.
  • An abstract method, which lacks a body, can be created using the abstract keyword.
  • A class must be abstract with the abstract keyword if it has abstract methods; otherwise, the class won't compile.
  • An abstract class does not necessarily need to contain abstract methods. Even if a class doesn't explicitly declare any abstract methods, we can nonetheless mark it as such.
  • Java doesn't support multiple class inheritance, so it's best to use an interface if an abstract class doesn't have any method implementations.
  • Unless the subclass is itself an abstract class, a Java abstract class must implement all abstract methods.
  • Unless an interface's methods are static or default, all of its methods are implicitly abstract. In Java 8, static methods and default methods were added to interfaces. For additional information, see Java 8 interface modifications.
  • Without even giving implementation of interface methods, Java Abstract classes can implement interfaces.
  • The Java Abstract class is used to offer default implementation or to provide a uniform method implementation to all subclasses.
  • If an abstract class contains a main() method, it can be run in Java just like any other class.

A real life example of data abstraction

  • Real-world data abstraction is comparable to a dashboard for an automobile.
  • It makes complex internal systems simpler while giving drivers access to crucial information like speed and fuel level.
  • This abstraction protects drivers from minute details so they can concentrate on driving.
  • It conceals the implementation, allowing the driver to see changes and the flexibility of the car.

Encapsulation vs Data Abstraction

EncapsulationData Abstraction
They are combining methods and data into one class, and limiting access to data members.By creating classes based on crucial traits and behaviors, complicated systems can be made simpler.
Control over who has access to private data. Exposing key functionalities while obscuring implementation details.
Access modifiers (such as private, protected, and public) are used to do this.Emphasizes the development of abstract methods and high-level interfaces.
Giving regulated access helps maintain the security and integrity of data. Reducing complexity, making it easier to maintain, and offering a clear interface.
Using public getter/setter methods and private fields to access and change data. Developing abstract classes or interfaces that have abstract methods that subclasses can implement.

Why we use interface in Java?

Here are some reasons why we use interface in Java:

  • To achieve abstraction: Interfaces can be used to achieve abstraction, which is an important aspect of object-oriented programming. By defining an interface, anyone can separate the implementation of a class from its behavior.
  • To provide multiple inheritances: Java doesn't support multiple inheritances of classes, but the developer can achieve a similar effect by using interfaces. A class can implement multiple interfaces, which allows it to inherit the behavior of all the interfaces it implements.
  • To define constants: Interfaces can be used to define constants that are shared by multiple classes.
  • To define callbacks: Interfaces can be used to define callbacks, which are methods that are called by an object in response to an event.
  • To achieve polymorphism: Interfaces can be used to achieve polymorphism, which is the ability of objects of different classes to be used interchangeably. By defining a common interface, the programmer can write code that works with any object that implements that interface.

How to declare interface in Java?

  • Interface declaration in Java is an interface that allows multiple inheritances of type.
  • It provides a powerful way of defining a contract between two classes, permitting loose coupling between the two parties.
  • Through interface declaration, complex relationships, such as inheritance and interface inheritances, may be established.
  • This helps create highly maintainable and extensible code that abstracts out major logic while avoiding deep nesting of classes.
  • Interface declaration also enables polymorphic behavior without the aggressive use of abstract classes or the need for extensive interface logic in the surrounding environment.
  • Interface declaration provides an efficient way to achieve flexibility in program development and code structure.

The relationship between classes and interfaces

  • The relationship between classes and interfaces in Java is an important concept to master when learning object-oriented programming.
  • Interfaces are basically contracts between a class and its implementers, that state which methods must be implemented within the class for it to be considered as fulfilling its obligation.
  • The interface defines what should happen, without getting into how it will be done.
  • This creates a layer of abstraction between the user and the developer, making the code easier to understand and maintain.
  • By separating data from its methods (encapsulating them in classes), software developers can create applications that best fit their particular requirements with far greater ease than if there were no such thing as interfaces.
  • In Java, classes implement interfaces in order to get specific behaviors or features that would otherwise not be available to them.
  • It's in this way that interfaces become so beneficial for object-oriented programming – they provide structure, simplify complexity, and ensure objects adhere to certain standards of behavior.

Nested Interface in Java

  • Nested interfaces in Java have multiple advantages and uses.
  • Nested interfaces are defined within another interface, and they can be used to group related aspects of a class together that have something in common.
  • Nested interfaces help create more logical class structures by decreasing the code needed.
  • Additionally, they allow developers to better encapsulate data and information, thus providing increased security against unauthorized modifications to code.
  • Nested interfaces offer improved scalability as well, allowing developers to work on larger projects like web applications without having all the code mixed up in one big file or class.
  • Nested interfaces are an important part of organizing and structuring coding projects when using Java, and their use can greatly enhance the efficiency of development efforts.


1. What is an abstraction in Java?

Java's abstraction feature allows for the simplification of complex systems by modeling classes with key attributes.

2. What is the use of abstract classes in Java?

In Java, an abstract class serves as a template for other classes, allowing them to inherit common attributes and functions.

3. Why abstract class is required?

In order to facilitate code reuse and organization, abstract classes are necessary to establish a common interface for related classes.

4. What are the advantages of abstraction?

Code simplicity, enhanced maintainability, and explicit interfaces are benefits of abstraction.

5. What is the difference between abstraction and encapsulation?

Encapsulation deals with restricting access to data within a class, whereas abstraction focuses on providing high-level interfaces.


In conclusion, learning Java Abstraction allows developers to focus on the important aspects of their programs and apps. Using abstraction saves time and effort because it reduces the amount of code programmers have to use. It also provides real-world solutions that can help to improve the overall quality of an application by getting rid of redundant tasks and focusing on essential elements. This type of abstraction does not require advanced knowledge and can be implemented with just a few simple lines of code. Moreover, Java Abstraction is approachable, user-friendly, versatile, and highly extendable which makes it perfect for any project. So, if you want to enhance your Java programming skills, don't forget to learn Java Abstraction!

About Author
Shailendra Chauhan (Microsoft MVP, Founder & CEO at DotNetTricks)

Shailendra Chauhan is the Founder and CEO at ScholarHat by DotNetTricks which is a brand when it comes to e-Learning. He provides training and consultation over an array of technologies like Cloud, .NET, Angular, React, Node, Microservices, Containers and Mobile Apps development. He has been awarded Microsoft MVP 8th time in a row (2016-2023). He has changed many lives with his writings and unique training programs. He has a number of most sought-after books to his name which has helped job aspirants in cracking tough interviews with ease.
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