Java vs. Kotlin – Which Language Should Android Developers Start With?

When it comes to Android development, most developers immediately think of Java. This shouldn’t come across as a surprise, according to the Tiobe Index the programming language is still a go-to choice for tech teams. Java has reigned supreme throughout the entire 2000s – until it got a rival to watch out for.

Java vs Kotlin: What Makes Them Different

In 2016, Kotlin was released – a specialized programming language for Android development. Since then, it took the market by a storm – in 2018, Google announced backing the language up as the primary one for Android development.

As for now, developers are wondering if a trendy language can gain traction and a steady following and how it scores against Java – a renown feature powerhouse. This post is a detailed Java vs Kotlin walk-through – their advantages, drawbacks, and use cases.

Java vs Kotlin: What Makes Them Different

At first glance, Java and Kotlin might seem alike as both are object-oriented and statistically-driven languages. While the two share similarities, the differences between them are as distinct. Here are some of the most notable distinctions between Java and Kotlin.

Nullable vs non-nullable exceptions

Java allows developers to manage null-variables, although not in the most efficient way. If a developer assigns a null to a variable, he will have to deal with a raised NullPointerExceptions.
In Kotlin, on the other hand, there’s no way to assign a null value to a variable. If a developer tries to override the system, there will be errors in the compilation process. The only way to handle null variables in Kotlin is by declaring val: Int? num=null

Long-running networks support

In Java, creating a multiple-thread network is impossible – a thread that contains high I/O operations will be disabled automatically. Before the introduction of Kotlin, Android developers had to create long-running networks in the background – managing them was tedious and complicated. 
Kotlin, on the other hand, supports the creation and management of intensive operations. The management process comes with its inefficiencies – if a CPU value reaches a certain threshold, the execution will be suspended although the threads will remain active.

Functional programming support

Java is fully based on the principles of procedural programming. As such, the older versions of the programming language did not offer functional programming support. Limited functional programming support has been later added to Java 8.
Kotlin offers a more extensive range of functional programming tools – high-order functions, lambda, lazy evaluations, and many more. The language is marketed as a mix of functional and procedural programming approaches.

Koltin has smart classes

Java developers have to check the cast type and variable manually to ensure it corresponds well to an operation that’s being performed. Kotlin, on the other hand, introduced the concept of smart casts, the type of which is defined automatically. In Kotlin, developers will not have to conduct manual immutable value checks either, using the ‘is-checks’ attribute instead.
In certain development aspects, Kotlin is modernized and more convenient than Java. However, both languages have their advantages and drawbacks – here’s a closer look at the pros and cons of Java and Kotlin.

Pros of Using Java For Android Development

Java is still the most popular software development language. Its following is hard to beat and the number of job openings on the market is skyrocketing. Why are software developers still so fond of Java when it comes to mobile app development? Here are the benefits of choosing the language as a part of a technology stack. 

  • Easy to learn. At its core, Java is designed to be simple and is considered to be a starting point for software developers. Other than that, there are so many high-quality courses and learning materials online that mastering the language is not one bit challenging. 
  • Cross-platform development. The language relies on ‘Write once, use everywhere’ as the dominant principle. Writing an app in Java allows moving the application from one operating system to another, promoting cross-platform availability and increasing the amount of reusable code. 
  • Huge open-source community. Java scores third by the number of GitHub contributors according to the platform’s official report. The number of practices and projects developers can use as the reference point is enormous – it helps improve the functionality of a future mobile app project.
Pros of Using Java For Android Development

Cons of Using Java in Software Development

For a long while, Java had a monopoly on the Android development market. Although developers were unsatisfied with the way certain aspects of the programming language operate, there was no other way to build mobile products. Now that Kotlin is around, tech teams no longer want to put up with the following Java cons:

  • Having to pay the commercial license fee for using Java 8. When releasing a new version of the language, the development team announced they will be charging teams for new updates. All the projects that want to install the latest Java updates will have to pay depending on how much daily active users the project has. 
  • Poor async handling. As for now, Java does not have a framework for handling asynchronous execution. Whatever mechanisms the language offers require tracking both the interface and the network calls simultaneously which is exhausting.
  • Convoluted data classes management. To build a basic data class with a couple of properties, a developer needs to define the fields of the future class, the ‘setters’, and the ‘getters’ and use several methods – ‘equals’ or ‘hashCode’. The entire process can drag on for dozens of lines, reducing the readability of the code.

Pros of Using Kotlin For Android Development

Kotlin is universally loved by developers – so much so that it placed fourth on the Stack Overflow’s ‘Most Wanted, Dreaded, and Loved Programming Languages’ List. Such a following doesn’t come for no reason – here are the benefits Kotlin brought to the Android development table.

Pros of Using Kotlin For Android Development
  • High readability. Kotlin helps reduce the amount of written code considerably, compared to Java. The language is respected for its to-the-point syntax. Writing the code and maintaining a released app takes less time when there are fewer lines of code to account for – the team efficiency grows faster. 
  • Java-interoperability. Kotlin’s development team made migrating from Java as easy as possible. The platform is compliant with all common Java tools, libraries, and frameworks. Software development teams can switch between languages freely within a single project.
  • Higher code consistency. This advantage derives clearly from the high code readability the programming language offers. A concise, compact code base protects developers from missing out on bugs during compilation and helps ensure error-free runtime.

Cons of Using Kotlin For Android Development

After taking a look at the positives of Kotlin, a developer should assess its negatives just as thoroughly before fully migrating the project. These are the most common drawbacks aspiring Kotlin developers and the teams that have already switched to the language have to face. 

  • A separate learning curve. Although Kotlin and Java have many similarities, getting used to a new language requires taking some time to hit the books. Business owners should account for team training expenses when mapping out a Kotlin migration. Java developers, on the other hand, need to look for learning materials and set time for education aside to master Kotlin. 
  • Compilation speed issues. As a newly-released language, Kotlin still has stability drawbacks. Generally, the language is faster than Java – however, when it comes to compiling clean builds, its compilation speed might fluctuate dragging the entire process for hours.
  • Fewer job openings and specialists for hire. Business owners, on the one hand, will have to deal with the challenge of finding a skilled Kotlin team. Developers, on the other, will not have such a wide array of job openings like the one that Java has to offer.

Why Should a Java Developer Learn Kotlin?

Java is still relevant in mobile app development – if you are new to software development, it should be the first language to be familiar with. Having said that, a professional Android developer has to consider learning Kotlin. The language is rapidly growing – it scored fourth by the growth rate in GitHub’s latest report. 

If it comes to comparing which language reflects the modern development practices better, Kotlin would dominate over Java. The programming languages of the future are likely to look exactly like Kotlin – specialized, clean, and efficient. 

In case you are wondering where to start learning Kotlin, here are a couple of resources to worth checking out:

  • Kotlin in Action – a go-to book for gaining an essential understanding of Kotlin’s main features. 
  • The Kotlin Website – the official learning platform empowered by the Kotlin development team. It has comprehensive tutorials on every feature of the programming language. 
  • Design Patterns Implemented in Kotlin – a useful practical GitHub repository that will provide Android devs with UI and UX inspirations.
  • Introduction to Kotlin. This Google I/O talk sums up the basic concepts of the programming language and will give a general understanding of where Kotlin is applied and how it’s different from Java.


Java has been around for a long while  – there’s no doubt the language is still here to stay. Although it’s unlikely for Kotlin to gain Android market dominance in the next five years, the nascent language shouldn’t be disregarded either. 
To be relevant in the industry and secure high-level job openings, Android developers have to start learning Kotlin and using the language in real-world settings. By investing in mastering Kotlin now, a beginning programmer can get up to speed with the language and become competitive in the Android development industry in no time.

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