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John Selawsky
John Selawsky

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Best Programming Languages You Can Learn as a Java Developer

Have you heard of Polyglot coders? They are those code developers who know more than one programming language, and they are really in high demand in 2021. Many job interviewers look for them because they’re the odd ones out who has more on their plate to give. New technologies arrive every year, and one language is often not enough to implement what is required.

A new language will give you space to be further creative with your codes since all of them have different concepts and cool new features to play with. Moreover, it can open new doors in your career and become a ticket to the best projects and teams.

In this article, you will find three programming languages Java developers should learn in 2021 and the reasons why. There is no surprise that all of these programming languages are JVM-based but they all have different qualities that make them unique and useful for a certain task.

Start with Proper Practice in Java

It may sound obvious, but before starting learning a new language, you have to verify your Java skill. As with every prominent technology, Java lives and develops, and you could miss some recent updates. Here is a list of some online resources you can use for your practice in Java.


CodeGym teaches you Java like you would play a game. So if you like playing video games, and you like being rewarded when you go up levels (who doesn’t, right?!), then this is the Java learning course you must go for. There are quests and side quests (RPG-players wink wink) and thousands of levels to learn Java. Moreover, you get to fix other people’s codes, learn the basics and the syntax, all on the way to a Junior Java Developer.


CodeChef is a non-profit competitive programming language learning website that gives you choice-based questions and urges you to continue coding till you get the accepted answer. The other outputs are also shown, which is helpful for you to understand where you went wrong in the first place.


Codewars is for developers who are somewhat advanced in their coding journey and no longer need to know the basics all that well. Codewars introduced katas or puzzle coding to the world. This makes it a new ray of sunlight in the otherwise dusty corridors of coding. However, for beginners, other sites would be recommended more.


Once again, better for intermediate or advanced programmers, Cyber-dojo uses TDD or Test Driven Development to challenge Java developers. The tester writes a test case, and the developer has to keep writing and rewriting the code till there are zero unsuccessful test cases left. Fun? Yes. Good for new people? Not really.

Top 3 Programming Languages Java Developers Can Learn in 2021

Learning Java can be one of the first steps to learning a new coding language. Learning how to solve Java-based problems and understanding the basics makes you able to learn other languages because many basic principles are similar. Three JVM-based languages in the list will complement your skills in Java and enrich your arsenal.


Scala was introduced in 2004 as the language that can run on Java Virtual Machine. Scala also follows the WORA principle; it supports some features of object-oriented programming and functional programming. Actually, Scala was created to fill the gap in the that-time Java version. In the beginning, it was considered to be that language that would end up replacing Java.

However, that did not happen, mainly when a few new and functional programming features got added to Java 8, such as the lambdas and the stream. Java regained its popularity and saved the leadership. Nonetheless, Scala is a helpful language to learn for Java coders. Apache Spark, an open-source engine for large-scale data processing, is written on Scala. White Big Data became a buzzword in digital technologies; it also opened a set of opportunities for the wise guys and language polyglots.

For this and other reasons, Scala has gotten an enormous fanbase over the last few years since several companies and new businesses started to use it. Uber, Amazon, Sony, Autodesk, Twitter use it, which has now turned it into popular coding languages. It is still not on the top: in 2020, it was ranked 17th by GitHub, based on the number of projects.

Anyway, Scala is still the language to learn for Java developers. Java is actively used for mobile development. The best Scala frameworks like Akka, Spark, and Play also help businesses take up Scala for web and Big Data solutions. If you plan to develop a career in one of these fields, Scala is a good choice.

What is more? Scala developers are so much in demand that to learn it well would ensure 120K USD as an average salary per year, which makes $10,000 per month. The amount can vary from country to country, and the highest Scala salary is in Norway. So, if you are a Norwegian Java developer looking for a new language, there is no reason to wait.

Recommended Book: Scala for the Impatient by Cay S. Horstman is a book for all beginners. It is lucid, has proper basics and syntax training, and will help you start with a bang.


Kotlin was started in the year 2011 by the JetBrains Team Blog, who are also the creators of IntelliJ IDEA, PyCharm, and several more high-ranking IDEs. Kotlin is JVM-based and can compile down Java easily. It is possible to use Kotlin in a Java or Android project from the middle of work, and staff will work out okay. This makes Kotlin your go-to best friend now with relief from NullPointerException and other very cool new features to boot.

However, Kotlin was not given much attention by most programmers till Google called it the best and official programming language for the sharpest Android Development in their 2017 Google IO. Since that time, the popularity of Kotlin has grown, and in 2019 it was ranked 4th by GitHub. Approximately 30% of developers use Kotlin, especially in mobile development.

While the world goes mobile, all programming languages that are used for mobile development are popular. Kotlin also can be used for IoT applications, web applications, and game development.

Along with Google, Kotlin is used by the following bug brands: Amazon, Netflix, task management tool Trello, Uber, and many others. They appreciate reliability, easy management, and high development speed.

The median salary of the Kotlin developer is $130,000, which is slightly higher than for Java. The reason is that in 2017–2020 the labor market struggled from the lack of Kotlin developers. However, since that time, many developers have entered this market. The salary is different in various countries: the highest amount a Kotlin developer can get in the United States, while in Australia and India the pay is lower.

Recommended Book: Kotlin in Action is a comprehensive guide to this popular programming language, and what’s better? The official website of Kotlin has all the answers to the exercises in the book.


Groovy is a JVM-based coding language that really adds to your Java programming with the brief codes, the def to define whatever you need, and great new features like multi-strings and collection literals. Groovy also helps reduce the development time with shortened expressions and the best unit testing Spock framework ever. Two languages are entirely compatible, but Groovy is more compact.

It is not easy to name some big companies that use Groovy: they only add it to the tech stack. Among them are the online money transfer services TransferWise and Starbucks.

Groovy is mostly used for the scripts above Java code. It is a perfect option for the often changing tasks. Tiobe index of language popularity ranked Groovy #19 in 2019, but this is an upward change.

Glassdoor reports the average Groovy developer can make $122,000 per year. However, the same service registers only 45 jobs in 2020 for this skill. It seems the employees prefer hiring so-called T-shaped specialists that are good in basic skill and can also perform effectively. In this context, T-shaped developers can combine Java and Groovy in their work.

Recommended book: Making Java Groovy is the book that you can definitely check out. It is so interactive and straightforward that it will have you writing Groovy scripts in a few hours!


It is a real professional aim for a software developer to become a polyglot coder and learn more than one programming language. With Java solely it is possible to build a career in the IT industry. Java engineers are in high demand, and the upward trend shows the market is hungry for more of them.

However, for those who want to grow up as professionals and create the T-shaped skills profile, there are three JVM-compatible languages: Scala, Kotlin, and Groovy. Each of these languages has its unique benefits, so combining two languages can make a better result.

First published at JavaRevisited.

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