Abstract Class vs Interface Java: Understanding Abstraction in Java

Developers consider Java one of the most popular programming languages. Despite its age and the rise of Python as an alternative, Java’s stability, and popularity guarantees that the language will be an integral part of development for years to come.

Programmers and developers who want to take full advantage of Java’s functionality should increase their understanding of the language and everything it can do. This greater understanding dovetails nicely with the concept of upskilling. To that end, we present a lesson on Java abstraction methods. This article will help you understand the differences between abstract class vs Java interface, two of the main building blocks of the Java programming language.

Now before we begin with abstract class vs interface java, let’s kick things off with some definitions.

Get a firm foundation in Java, the commonly used programming language in software development with the Java Certification Training Course.

What is Abstraction? A Refresher

The IT world generally defines abstraction as the process of hiding internal details of implementation and only showing essential functionality things to the user. To put it in non-technical terms, you don’t need to know how sausages are made before eating one. You just want to know the steps required to cook it properly. How it got to your plate is unimportant.

Put another way, the abstraction process focused on an automobile means you can see and interact with the steering wheel and gas and brake pedals. You don’t need access to the fuel injection system or the serpentine belt.

There are two different methods of achieving abstraction in Java, and that’s where we are going next to better understand abstract class vs interface Java.

What is an Abstract Class in Java?

An abstract class is defined as a class that’s declared with the “abstract” keyword. It is a collection of common subclass characteristics that should include at least one abstract method. An abstract class can have multiple concrete methods. Programmers using Java 8 and later can also incorporate default and static methods.

An abstract class cannot be instantiated, meaning you cannot create an object with it.

Programmers use abstract class vs interface Java when they need:

  • Default functionality for subclasses
  • Templates for future specific classes
  • Defining a common interface for any subclasses
  • Code reusability

Before we begin with the abstract class vs interface in java difference, let us understand more about the interface in Java.

What is an Interface in Java?

An interface is a blueprint used to implement a class. It is a collection of abstract methods and contains no concrete methods, unlike abstract class. However, the interface offers full abstraction in Java, something that abstract classes cannot do.

Like a class, an interface can contain methods and variables, though the declared methods default to abstract.

Interfaces cannot be instantiated, though abstract classes that implement interfaces can.

Programmers use interface when they need:

  • To achieve abstraction
  • To support a dynamic resolution at run time
  • Achieving loose coupling
  • Separating a method’s definition from the inheritance’s hierarchy

Now let’s explore the primary differences between abstract class and interface.

Full Stack Java Developer Course

The Gateway to Master Web DevelopmentExplore Course
Full Stack Java Developer Course

What is the Difference Between Abstract Class vs Interface Java?

The best way to quickly and easily compare abstract class vs interface Java is to illustrate the information in a table. So here we go:

 

Abstract Class

Interface

Access Modifiers

Can have access modifier

Does not have access modifiers, and everything defined inside is assumed to be a public modifier

Constructors

Can declare constructors and destructors

Cannot declare constructors or destructors

Data Fields

Can have data fields

Cannot have data fields

Data Member Accessibility

Can have any type of class member (e.g., public, private, protected)

Can only have public members, by default

Defining Fields

Users can define both fields and constants

Cannot define fields

Extension Limits

Extends just one class or one abstract class at a time. Can extend another regular (or concrete) class.

Can extend any number of interfaces. However, it can only extend interfaces.

Implementation Speed

Faster than the interface

Interface is slower and requires extra indirection or dereferencing

Instantiation

Cannot be instantiated, but it can be invoked if main () exist

Cannot be instantiated, as it is absolutely abstract

Keywords Used

Abstract keyword used to declare the abstract class. Also, the abstract class can be extended by using the keyword “extends”

Interface keyword used to declare interface. Also, interface can be implemented by using the keyword “implements”

Methods

Can have abstract and non-abstract methods. Can have default method implementation

Can only have abstract methods, though, since Java 8, it can also have static and default methods. Cannot have implementation due to interfaces providing pure abstraction

Multiple Inheritances

Can have only one abstract class

Can implement several interfaces

Structure

Abstract methods only

Abstract and concrete methods

Variable Types

Can have final, non-final, static, and non-static variables

Can only have final and static variables

When It Should Be Used

Use when several implementations of the same type share common behavior, Additionally, use it if you require a base class.

Best used when various implementations share only method signature. Also, a good choice when your classes need additional behavior or dependency injection.

How to Learn More About Java and Javascript

There are so many things to learn about in both Java and JavaScript. Fortunately, there are plenty of resources available to help bring you up to speed. But rather than scouring all corners of the internet to find different courses, you can visit Simplilearn and find a wide selection of courses and free resources to choose from.

First, check out Simplilearn’s Java Certification training course. This advanced course is designed to guide you through Java’s concepts, starting from introductory techniques and finishing up with advanced programming skills. The course also teaches you about Core Java 8, operators, arrays, and methods while giving you valuable hands-on experience in JDBC and JUnit frameworks.

You can take the course through self-paced learning, corporate training, or Simplilearn’s unique and highly successful Blended Learning option. Regardless of the option you choose, you will be assured of the best Java programming training available.

The course gives you everything you need for Java certification, including 70 hours of blended training, hands-on coding and implementation of two web-based projects, 35 coding exercises related to Java 8, and the Hibernate and Spring frameworks. You will also enjoy the benefits of lifetime access to self-paced learning resources, and of course, your Java certification certificate, awarded once you meet the criteria.

If you’re ready to boost your developer skills to the next level, Simplilearn also offers a collection of Master’s programs perfectly suited for Java and JavaScript programmers. There’s the Full Stack Java Developer Master’s program, which is designed to give you a solid, working understanding of front-end, middleware, and back-end Java web developer technologies. You will acquire the skills needed to build an end-to-end application, test and deploy code, store data using MongoDB, among other projects. The Full Stack Web Developer - MEAN Stack master’s certification training gives you comprehensive knowledge of software development and testing technologies such as JavaScript, Node.js, Angular, Docker, and Protractor. However, if you’re leaning more towards automation testing, you should look into the Automation Test Engineer Master’s program. This program gives you a thorough knowledge of today’s relevant software testing technologies. You will learn about Selenium Web Driver, TestNG, Maven, AutoIT, Selenium Grid, Appium, and Docker, and how they can help you develop a robust testing framework.

According to Indeed, Java Developers can earn a yearly average of USD 104,463, including USD 5,000 cash bonuses. Glassdoor reports that Java Developers in India can earn an average annual base pay of ₹457,826.

And Java’s not going away anytime soon! The demand for Java developers remains strong, although the language is 25 years old (an eternity in the world of IT!). A career as a Java developer brings job stability and excellent benefits, especially when you understand the nuances between abstract class vs interface Java. If all this sounds appealing, then visit Simplilearn and get started on a better career today!

About the Author

John TerraJohn Terra

John Terra lives in Nashua, New Hampshire and has been writing freelance since 1986. Besides his volume of work in the gaming industry, he has written articles for Inc.Magazine and Computer Shopper, as well as software reviews for ZDNet. More recently, he has done extensive work as a professional blogger. His hobbies include running, gaming, and consuming craft beers. His refrigerator is Wi-Fi compliant.

View More
  • Disclaimer
  • PMP, PMI, PMBOK, CAPM, PgMP, PfMP, ACP, PBA, RMP, SP, and OPM3 are registered marks of the Project Management Institute, Inc.