Kotlin vs Java: What is Better for Android Development?


Java is (or rather, was) the main programming language for the Android platform. To the coder who types the painfully familiar operators and functions in the editor day-by-day, the process of creating the software code has become no more complex than the process of writing an essay in English. It really is that simple. One might wonder - why should we look for something better? After all, Java is a time-tested, statically typed programming language with a huge technical support community and a fairly low input threshold (at least it can be easily mastered by the vast majority of technical students, with a basic knowledge of C). Do you think mobile developers are gradually moving to the new language without reason? Not at all! So what should you choose: Kotlin or Java for Android development? In this article, we will review the main differences between Kotlin vs Java. Will Kotlin replace Java in the future? Let’s look at the advantages in using Kotlin for Android development and the cases that are better left for coding with Java.

Explaining Kotlin

The history of the Java vs Kotlin confrontation on the Android platform is absolutely similar to the history of Objective-C vs Swift, in the case of iOS. If you are familiar with the nuances of the last two languages, then you already know that the mechanism that "launched" the process of creating the now very popular Swift was the search for a solution to create a simpler, more readable, and concise program code.

Kotlin was created for exactly the same reason. Developers sought to create a powerful modern language, with clear and compact syntax, a high level of security and reliability, strict typing, and fast compilation. It is engineered to work alongside Java/C++ and the libraries written in these languages. This allows them to continue using the previously created tools and to include Kotlin in existing development processes seamlessly. The recently released stable version of the language is as close to reaching the initial goals as possible. For instance, some code constructs, which would require more than a dozen lines in Java, fit on 3-5 lines in its counterpart.

Let us look at the bare facts. Well-known technology company, JetBrains, started designing Kotlin back in 2011 and the next year, the project was open-sourced. It is statically typed, like Java, and can become the basis for both object-oriented and procedural programming. Though Kotlin’s syntax is not directly compatible with Java code, it was designed from the start to be interoperable. Moreover, Kotlin contains the complete set of operators and functions for functional programming, which is currently widely used. The ease of learning is among the top benefits but, of course, as with any novelty (even those as innovative and advanced as Kotlin is), the development companies will need some time to implement this programming language into commercial projects.

Six years into development, the knowledge of Kotlin is no longer considered to be "cosmic" and incredible, so mastering its basics is already a prerequisite when hiring for most successful employers in the field of mobile apps for Android (especially in outsourcing). One should note, though, that this movement only started recently – after Google announced Kotlin as the new primary programming language for the Android platform (Google I/O conference, May 17-19, 2017).

Read also: Google I/O 2017: The Most Important Announcements

Now, to avoid seeming completely biased, let us consider the pros and cons of Java and Kotlin and summarize in which cases each of them will be preferable.


Kotlin vs Java comparison: 8 Reasons to Prefer Kotlin over Java

Not departing from the idea that Kotlin is the future of mobile development for Android, let us review its main advantages.

  1. Simpler learning. Learning Kotlin, even with zero knowledge in the field of mobile development, is much easier than learning Java. In order to write a simple application (but not as simple as "Hello, world!"), no more than a couple of hours is required. Perish the thought that it will be long. Moreover, if you previously coded in C# or Java, the transition to Kotlin will be practically painless. Fortunately, JetBrains developers put a lot of effort into creating documentation, and it is so detailed that the basics of this programming language can be quickly mastered by schoolchildren. The Android Studio development environment provides a complete adaptation of the tools that are used in Kotlin (in fact, you need not worry about the incompatibility of this IDE with the language). Another undoubted advantage is the reverse support for Java. That is, developers can connect to the same project files in these two languages without worrying about their possible incompatibility. You simply use the functions or operators from the Android libraries for Java in the same project, and they work together seamlessly! This fact is especially pleasing for newcomers who previously practiced Java. After all, they can now clearly ensure the correctness of the code they create, simply by supplementing the undeveloped parts of the program with Java libs.
  2. Code reliability. Any programmer who has tried to code something more complex than a regular calculator encountered situations where the syntax looks correct but, for some reason, the compiler still does not allow it to be launched. One of the main reasons for this is null pointers, the incorrect use of which results in runtime errors. Null pointer exceptions have brought down a lot of seemingly flawless code. In Kotlin, virtually all possible sources of such references were eliminated, which is the main advantage of Kotlin vs. Java. Thus, the compiler will not allow the use of variables with prior unassigned values. So, what if the developer needs to refer to such a variable? In order to announce a variable with a nullable value, a question mark is placed at the end of the declaration. In this case, if you use such variable, the compiler will check its value each time the code is executed(whether or not it was initiated), thereby increasing the security of the generated code. There are other options. For example, in order to access such links, Kotlin developers can also use blocks of ‘if-else’ (or just ‘if’), a safe call ‘.?’, elvis-operator ‘?:’ and ‘!!’ operator.
  3. Extension functions. To date, Java has no implementation plans for extensions; however, you will appreciate their advantages if you have previously worked with C# or Gosu. Such functions are designed to extend the capabilities of classes, without the usage of inheritance and Decorator patterns, meaning developers can cause them directly from instances of a class. This solution allows you to not only modify the class itself but, at the same time, complement its instances if needed. In addition to functions, Kotlin also has extension properties that work in a similar way and are very comfortable. In the case of working with Java to implement similar needs, you would need to use utility classes from java.util.Collections, which, in turn, entails long, pre-existing code lines that are quite difficult to read. Of course, developers can use auxiliary tools from Android Studio, such as auto-completion, to simplify such code, but this solution is complex and time-consuming. Why bother then? Employ Kotlin!
  4. Higher-order functions and lambda expressions. Higher-order functions are typical of many modern languages. These are functions that can either accept other functions as arguments or return some function as a value. The reason they are needed probably does not require a detailed explanation. They allow for the creation of extremely concise programs, regardless of the complexity of the used logical structures. The code written using these functions looks incredibly elegant. What about Java? Unfortunately, nothing joyful here. In Java applications, you would be guaranteed to use many more commands to do the same. What about lambda expressions? In the event that the function was not declared before but, nevertheless, was called directly from another function, it is called a lambda expression. These expressions carry the same practical benefits as higher-order functions.
  5. Data classes. Kotlin contains a very useful feature that is not available to Java developers: data classes, another of the main differences between Java and Kotlin. In applications, classes are often used as structures for storing data. The functionality of such classes depends directly on the stored information, and they are denoted with the ‘data’ prefix. What does this mean, in practice? First of all, it saves a lot of time, which is impossible when looking at Java. In particular, you will need to use ‘get’ and ‘set’ methods when declaring each field, which makes the code less easy to read and simply distracts from the main tasks.
  6. Data consistency control. Declaring the properties of a class, you can make them mutable, denoted by the keyword ‘var,’ or read-only by the keyword ‘val.’ In practice, using this system helps to minimize the number of manually entered commands required to ensure consistency of data under the influence of multiple threads, which decreases the risk of errors due to inattentiveness. With Java, there is something similar, namely the keyword ‘final,’ the use of which, however, provides much less flexibility for developers.
  7. Co-programs. Version 1.1 brought a lot of useful innovations for developers of mobile software for the Android platform and, among them, such features as co-programs (coroutines). Coroutines were designed to facilitate the creation of asynchronous code, which is necessary to ensure continuous operation of the application during the execution of I/O operations. In the case of Kotlin, developers write code as if it were synchronous, and the compiler then independently transforms it, eliminating the need to manually block the threads (suspend co-programs). The price for this solution is notably less. After all, the parallelization manager is included in the language libraries, thus entailing a significant reduction in the project costs.
  8. Type aliases. With version 1.1, such feature as type aliases appeared. Type aliases are alternative names for existing types, which make it possible to shorten the summons where such types are used (all this, again, to increase the code readability as much as possible).


Kotlin vs Java: Where Java is Undeniably Better

Although Kotlin has a lot of useful characteristics suitable for modern language, there are still situations in which Java is more preferable. Let us consider them in more detail.

  • More compact apps. Practice has shown that applications created on Kotlin are heavier, compared to full analog in Java. This means that some applications that imply the execution of complex computing processes in their code can be quite slow on user devices with low technical specs. But not everything is this unambiguous, and this is likely not to last forever - we are sure that, in new versions of Kotlin, developers will eliminate this shortcoming.
  • Faster build process. The second, albeit not very significant advantage of Java, in comparison with Kotlin, is the accelerated assembly within Gradle (we know first-hand how infuriating it can be when assembling large projects takes a lot of time). Although to be completely honest, Gradle is generally slow on its own.

Kotlin vs Java Performance

Now, let’s review the question of efficiency. In cases of traditional programming languages, the performance of the application depends on many factors such as developer skills, the simplicity of the application’s business logic, level of the compiler’s adaptability to real hardware, etc. When comparing Java and Kotlin, the code is compiled into the intermediate bytecode which is then executed by JVM. Thus, comparing completely identical applications on Kotlin and Java, we may conclude that the efficiency of both is comparable and depends solely on the performance of the specific JVM implementation. Current Android runtimes - ART - are considered to be the best existing JVMs and a great step forward from the initial Dalvik runtime.



Let us sum up the advantages and disadvantages of this pair of languages. The transition to a new language is not an exciting and joyful event for every developer. Some of them, already have found for themselves the best tools and ways to implement program code, do not want to look for something newer and better. There is some base for this conviction. Of course, to learn a new programming language, as well as something new, in general, you will have to spend a lot of time on the project. In order to be proficient in creating a commercial project for business on Kotlin, no less than a month is required. In addition, there will always be a risk that some of the team members might not manage to adapt to time; however, if you are a beginner or an evolving developer who is looking for new ways to create mobile software, then we are confident that the efforts spent on studying will fully justify themselves (especially in the case of creating software for startups). As a result, you can create a concise, well-readable code that is ideal for teamwork, and that’s not all. After all, that, if necessary, you can always remake your application under the Java language with minimal losses.

In case you have an idea for a startup that requires the implementation of a complex software solution, but no experience or dedicated resources required for Kotlin development, we can offer you the services of our experts. We are Applikey Solutions - an outsource development company with years of expertise in mobile and web development, software design and QA. Reach us today and let us success together!

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