Kotlin vs Java – detailed comparison

Last checked and updated on July 2, 2022

Java vs Kotlin

Technology, arguably more than any other industry, moves at a tremendous pace. What was cutting edge yesterday can be obsolete tomorrow. This applies to programming languages, although some names have endured longer than anticipated.

Java is arguably the best-known coding language, if only based on longevity. While Apple and iOS do not typically program apps and software with Java, it has remained foundational for Android-centric coding.

As discussed though, the technology industry never stands still and new programming languages arise all the time. One comparatively recent addition to the pantheon that is making a lot of waves is Kotlin. There is plenty to love about Kotlin, but how does it really compare to Java?


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What are Kotlin and Java?

Kotlin and Java are programming languages designed for writing code by programmers. Java was a game-changer when initially launched in 1995, and it retains a loyal audience today. While Java started small, many websites and applications now rely heavily on the language. 

Some of the most popular uses of Java are:

  • Developing Android apps
  • Programming hardware
  • Analysing data
  • Creating server-side tech and Enterprise software

Java is regularly updated like all software, and installing the latest version is advisable. V17 is the current edition, and you can find it available for download on the official Java website. It is inadvisable to use an outdated version of Java, as doing so could lead to a security risk.

Java laid the foundations for new languages to follow, and many struggled to escape its shadow. One name that is familiar to Android developers, however, is Kotlin. Open source since 2012, Kotlin has earned a healthy and impressive reputation among the coding community. So much so that Kotlin is considered the future of Android app development by some commentors. 

In a nutshell, Kotlin is a streamlined version of Java. That doesn’t mean that a complete novice can work with Kotlin, though. In fact, if you have never worked with coding before, Java remains the foundational text to study. Once you understand Java, you’ll be able to make the most of Kotlin.   

What’s the difference between Kotlin and Java?

As discussed above, both Java and Kotlin are programming languages – and Kotlin could be considered a natural advance on Java. As the two languages are not from the same manufacturer, though, there are some key differences to note. 

Some of these variations could be considered advantages of one language over another –usually working in favour of Kotlin. We’ll discuss that in more detail shortly. In the meantime, here are the fundamental differences between Java and Kotlin.

Unlike Java, Kotlin incorporates an extension function
Java makes implicit conversions possible, unlike Kotlin
Kotlin does not work with null variables and objects, which is a regular issue with Java
Java only supports object programming. Kotlin offers object programming and functional programming 
Java offers more third-party components and plug-ins and supports static members, while Kotlin does not
Kotlin is easier to deploy and shorter to write code within – for a start, there is no need to use semicolons in Kotlin

It’s worth remembering that, without Java, there would be no Kotlin. This means that a fundamental understanding of Java is essential to benefit from Kotlin. There is plenty to love about both languages, but more and more coding professionals are embracing Kotlin. The differences discussed above are among the key reasons why.

Benefits of each – when would you choose one over the other?

We have mentioned a handful of times that some coders prefer Kotlin to Java. There are benefits and drawbacks to both languages, though. Let’s review these in the table below.

JavaJavaKotlinKotlin
AdvantagesDisadvantagesAdvantagesDisadvantages
Effortlessly reliable and constantly offers high performanceToo limited to function efficiently with Android APIAllows extraction of common codebases in a multiplatform frameworkCompiles slower than Java
Automatically conducts checks for errorsRelies more on manual work than automationPre-built safety and support from null values – a considerable advantage over JavaNot yet as commonplace as Java, so help can be harder to find
Plenty of resources for research and insight are available onlineBig data processing means it can feel a little sluggish in some scenariosCoding is shorter and more user-friendly than Java and faster to writeMore declarative than Java
Almost all developers and coders are skilled in JavaRequires a great deal of memory for processingAutomatically breaks larger apps down into smaller layersJava will not check code written in Kotlin, so errors may arise
Countless third-party libraries and plug-ins are available Code can be maintained to scale 
Welcoming of standard and reusable coding  Compatible with a range of varying function types 
Flexible enough to accommodate multitasking Open to third-party extensions from developers 
Library navigation is intuitive and straightforward Data classes simplified to the point of automation 

Based on this data, you can make an informed decision as to which language will meet your needs best. Of course, there is nothing to say that you need to choose one and remain 100% devoted to this language at the expense of the other. One of the great things about Kotlin and Java is their interconnectivity.

Speed and performance – which is better?

Java has clung to its reputation as the leading coding language for so long due to its excellent performance. There is no denying that while rivals – including Kotlin – can offer more bells and whistles, Java remains reliable. 

In addition, Java is a little faster when compiling than Kotlin. Not by much, but that difference is there. Kotlin is starting to rival Java for speed with each update, though. It’s also worth noting that Java takes up a great deal more memory than Kotlin. This may start to lead to slower performance on older, creaking hardware.

Popularity – does Kotlin or Java have better adoption?

There is no denying that Java holds the upper hand in terms of use and adoption at the time of writing. 35% of app developers use Java, while just 8% have made the transition to Kotlin so far. Statistics do not always tell the full story, though. 

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A good way to assess the popularity of Java and Kotlin – and how this will pertain to you – is to consider what popular apps are created with each language. Take a look at the below and see if one particular language captures your imagination based on previous users.

Kotlin appsJava apps
TinderSpotify
NetflixTwitter
AirbnbCash App
PinterestLinkedIn
Uber 

As we mentioned at the very top of this article, however, the world of tech moves quickly. Kotlin is a considerably younger coding language than Java and is still forging its path and finding its place in the industry. 

Java is the biggest dog in the yard, but it’s looking over its shoulder for the first time in a while. The full embrace of Kotlin by numerous cutting-edge brands suggests that we have not heard the last of this language.

The bottom line: what’s better?

Better will always be a subjective term. When it comes down to choosing between Kotlin and Java, your choice will likely depend on what you are writing code for. Naturally, your pre-existing comfort level with either language will also play a part.

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If you’re learning to code for the first time, Java is the ideal choice. Understanding Java will unlock the capacity to make the most of Kotlin, not least because the two languages are often interchangeable. 

Equally, stick with Java if you’re not entirely comfortable with coding and may need professional help. A much larger global community of Java experts can pitch in with advice or support. As Kotlin is comparatively new, professionals are fewer and further between.

Many professionals will tell you that Kotlin is the future of code, though. For a start, this is because Kotlin is so much more efficient. You can write code in half the time it would take in Java, and it’s hugely easy to read. Most everyday features of Java are also now available in Kotlin, and it’s typically easier to maintain. 

Only you will know what language is best for your needs. At the risk of sounding like we’re hedging our bets, learning both Java and Kotlin is highly advisable. However, all signs point to Kotlin eventually dethroning Java as the global programming language of choice once you have done so. Embracing this language now will futureproof any app or website.

FAQ

Why Kotlin over Java?

Java remains the more popular programming language overall, but an increasing number of Android developers prefer to use Kotlin today. Kotlin can perform most of the same tasks as Java quickly, using considerably simpler and more concise code. Kotlin can also co-exist with Java and use commands initially written in this language – and others. Essentially, Kotlin could be considered a streamlined evolution of Java.

Why Java is better than Kotlin?

Java remains the industry leader in code, especially relating to Android apps. While an increasing number of developers are embracing alternatives, most notably Kotlin, Java will always remain the default choice. Coding with Java ensures that work will always remain compatible with any needs.

Why Kotlin is better than Java?

Kotlin does almost everything Java can, but usually faster and easier. Kotlin also resolves some of Java’s biggest pain points. The most notable are type safety and the ever-dreaded null references.

How is Kotlin different from Java?

The most significant difference between Kotlin and Java is the time it takes to write code. What takes some fifty lines in Java can be achieved in just two or three in Kotlin. In addition, Kotlin resolves some of the common issues that plague Java users.

Kotlin vs Java, which is easy to learn?

Kotlin is easier to use, but Java is easier to learn. Java is a foundational coding language, and most rivals – including Kotlin – have followed in its footsteps. It’s a case of evolution, not revolution. If you try to learn Kotlin before Java, it’s akin to running before you can walk. By mastering Java initially, you will take to Kotlin much faster.

Which is better for Android development, Kotlin or Java?

How do you define better? Java is arguably still the dominant force in Android development, if only because it’s the most commonly used coding language and best-known name. Many developers prefer to use Kotlin in 2021 because it is much faster to write code in this language. Kotlin has also ironed out a wide range of pain points and common issues that have plagued Java users for years.

How to convert Kotlin to Java?

Converting Kotlin to Java is a two-step process. The first is to compile the code using the code kotlinc. So, if you want a file name in Kotlin named Creative.kttype kotlinc Creative.kt
 
Next, decompile the Kotlin file into Java. Use FernFlower for this, using the command java -jar fernflower.jar CreativeKt.class

How to convert Java to Kotlin?

IntelliJ IDEA is the easiest way to convert Java into Kotlin. Just create a Kotlin file and paste the Java code into this document. This will bring up a dialogue box that asks if you’d like to proceed – click yes in this instance. Now the Java file is open, head into the Kotlin main menu and select Code, then Convert Java File to Kotlin File.

Why Java takes more memory than Kotlin?

The memory discrepancy between Java and Kotlin revolves around fractional components of numbers. In Java, these are saved as primitive types. Kotlin, on the other hand, boxes fractions as Integer objects. As Kotlin also uses fewer lines of code than Java to perform the same task, Kotlin will require less memory.

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