Java vs Kotlin - Comparison & Use Cases for Elegant Android App Development

Businesses seeking custom Android app development often face a dilemma these days when choosing a technological stack. Whether to choose Java or Kotlin? Although Kotlin’s patronage grows daily, Java’s superiority as the de-facto Android app-building language remains omnipresent. Many notable businesses have moved their applications from Java code to Kotlin, while some continue to swear by the mature programming conventions and extensive support available for Java-based Android programming.

The competition between Java and Kotlin is quite similar to that of Obj-C and Swift. Kotlin was intended to overcome the inherent shortcomings of its Android programming predecessor, Java, while Swift was developed with a similar intent w.r.t. its MacOS and iOS-coding predecessor Obj-C. To settle the dispute and dilemma between choosing Java and/or Kotlin one must compare their merits and demerits on the same grounds, in great detail, as we have done below.

About Java

Java is an open-source, high-level OOP and Procedural Programming language based on a C, C++ foundation. It needs very little introduction as it has revolutionized OOP from the mid-90s since its inception by James Gosling at Sun Microsystems, and is now used to script most software applications and embedded hardware coding. It was the de-facto Android programming language for developers up until the emergence of Kotlin.

Developers across the world have sworn by Java for its use of classes, objects, abstraction, inheritance, interfaces, reflection, singleton, encapsulation, and polymorphism, among other OOP perks.


Syntax (code readability)

Java code is easy to read as it has been around longer and has a widespread support community.

E.g.: A simple calculator program in Java.

public class ClearBridge {

public static double calculate (double a, String op, double b) throws Exception {

       switch (op) {

               case "add":

                       return a + b;

               case "subtract":

                       return a - b;

               case "multiply":

                       return a * b;

               case "divide":

                       return a / b;


                       throw new Exception();




Java makes up for its verbose syntax with its OOP attributes. Inheritance allows one to extend the properties of existing classes; so, developers do not have to redefine class properties again when coding newer blocks and modules, just ‘extend them’.


class KingdomAnimalia



class Bear extends KingdomAnimalia



Function implementation

As an OOP language, Java allows us to define standard library functions that are methods built-into the Java Class Library. Among standard library methods, developers have the option of using public methods and inherited methods such as ‘java.lang.reflect.Executable’, ‘java.lang.reflect.AnnotatedElement’, etc. to interact and manipulate the data of various classes.

Java uses access modifiers to protect the original data, while inherited classes and their functions work with dynamic parameters- a massive boon of Java’s OOP-based encapsulation properties. Java also allows developers to get creative with the help of user-defined functions which comprises an access modifier, the static keyword, and its return type.


modifier static returnType nameOfMethod (parameters) {

   // method body


Polymorphism also has a special role when it comes to defining complex methods for Android apps using Java code. Polymorphism works in tandem with inheritance to allow developers to use objects in child (inherited) classes concerning the parent class.

‘Method Overriding’ is the process by which developers can manipulate methods depending on whether it has been invoked by an object of the parent class or the child class. Method overriding is used for runtime polymorphism.


class Vehicle{  

  void run(){System.out.println("Vehicle is running");}  


class Train2 extends Vehicle{  

 void run(){System.out.println("Train is running safely");}    

 public static void main(String args[]){  

 Train2 obj = new Train2();;  



Output- Train is running safely

On the other hand, ‘Method Overloading’ is the process by which developers can manipulate methods in different ways depending on the arguments they pass through it. It allows a class to have multiple methods with the same name for better readability but allows developers to pass different types of parameters through it.


Overloading by the no. of parameters-

add(int, int)

add(int, int, int)

Overloading by the data type of parameters-

add(int, int)

add(int, float)

Overloading by the sequence of the data type of parameters-

add(int, float)

add(float, int)

Java methods ALWAYS need a class object to be implemented and pass parameters by value or by reference. Also, Java does not “directly” support nested methods (higher-order functions), but nested methods can be invoked in Java 7 or older versions by defining local classes and anonymous subclasses. In Java 8 and above developers can of course use the lambda expression for nested functions.


Unlike many other programming languages including C and C++, when Java is compiled, it is not compiled into a platform-specific machine, rather into platform-independent bytecode. This byte code is distributed over the web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on. Java compiler generates an architecture-neutral object file format, which makes the compiled code executable on many processors, as long as a Java Runtime Environment is present.

It needs to be noted though that although developers need the Java Development Kit for compiling programs, the programs do not rely on the standard JRE and JDK compiler when executed in the Android platform environment.


Originally, Android application developers relied on the Oracle Java Mobile Information Device Profile and Connected Limited Device Configuration for mobile applications. Android applications utilized the Dalvik Virtual Machine thus availing Ahead-of-Time compilation for apps that convert the byte code to machine code.

However, since its version 7, Android switched its Runtime Environment to the OpenJDK, which introduced a Just-In-Time compiler with code profiling to the Android Runtime (ART), which allows it to continuously improve an Android app’s performance as it executes. The JIT compiler complements ART's current Ahead of Time (AOT) compiler and helps improve runtime performance with better garbage collection.

Error handling

While building apps in Android Studio, developers rely on try-catch statements to specify routines where throwable exceptions are necessary to avoid runtime errors.

Generally, Java’s compiler time and runtime error checking are sufficient to rectify bugs in the code. developers can also utilize Java’s preemptive error-handling capabilities with the newer IDE’s.

Memory Management

Developers love Java’s multithreading capabilities for better memory utilization and management with Android programs. Multithreading essentially breaks down data-intensive complex operations into smaller operations with individual threads. Java’s platform-neutral architecture and multithreading work hand in hand to run these threads (sub-operations) simultaneously, which paves the way for better application performance on systems with multi-core processors.


Build-cycle advantages

  1. Code reusability. Write methods once and call them from anywhere.  
  2. Android was engineered to be a java-based OS, which also allowed developers to write programs in C/C++.
  3. Java’s OOP approach to app development allows developers to leverage inheritance, polymorphism, abstraction, encapsulation, method overloading, and overriding.
  4. Java offers a huge collection of open-source libraries such as  Apache Commons, Google Guava, JUnit, which ultimately helps developers reduce development time and the lines of codes they’ll need to script.
  5. Java is synonymous with Progressive Web App development. Developers still blindly trust Java when it comes to developing Cloud server-based apps with Java extensions for seamless execution on a diverse array of platforms.

Build security

One of the many benefits of OOP is ‘modular’ programming, wherein one can independently write and test modules and then integrate them as a part of a large application program, thus,  producing stable programs and iteratively launching new updates.


The OOP-granted modular programming aspect further comes in handy for Android developers w.r.t. feature extensions that aid with Android app scalability. The ability to produce stable program modules means your business application can also scale up indefinitely with the changing trends of the market, as long as your resources permit.

Platforms supported

We credit Java as the pioneering language that promoted the ‘write once, run anywhere’, programming ethic. Java has been used to program apps for the web, mobile, desktop, and even embedded circuitry in appliances for its hardware-independence. Today, Java-based Android platforms are executable across a broad array of platforms including next-gen IoT hardware and Cloud-oriented applications.

The cross-platform operation enabled by the Java Virtual Machines allows one to write programs targeted for the Symbian, Windows, Mac OS, and iOS platforms as well.


Migrating multi-module Android applications written in Java to any other language is a hassle-free process with Android Studio. Android Studio permits the importing and migration of Java projects developed in other IDEs such as Eclipse and IntelliJ( the Java IDE on which Android Studio is based, developed by the developers of Kotlin- JetBrains). Java’s easy-to-read code and similarities with C/C++ also reduce time consumption and complexity when porting to Obj-C or Swift, for native iOS deployment.

Support community

The Java support community is quite forthcoming in assisting each other with creative and intuitive problem-solving. Numerous support forums come together to assist developers with programming, troubleshooting, and advisory. You can compare notes, and find suggestions for open-source and premium Java libraries and tools that help uplift Java Android programming standards.

There is also no dearth of knowledge material on Java. Such a proactive support community is critical for your application’s success and global marketability.

Type of applications

The Android SDK offers standard Java libraries that handle data structuring, math, graphics, networking software for mobile, desktop, and large-scale industry servers. For a language that has already peaked, Java continues to innovate recently expanding into platform-independent, Cloud &  IoT application development.

Needless to say, Java is entangled with Android application development as the platform was built with Java. Some of the most commercially notable Android applications developed in Java today are Spotify, Twitter, Signal, etc.

About Kotlin

Kotlin is a statically typed, general-purpose programming language. for Java Virtual Machine (JVM) and JavaScript. It was developed by JetBrains, (the company behind the IntelliJ IDE) as an open-source programming language and now finds widespread application as a bonafide Android app development language, besides Java,  and is described as a general-purpose language.

Rather, Kotlin’s interoperability makes it easy to build new features, extend platform support, and perform migrations of older Java-based legacy Android apps.

As an OOP language, Kotlin offers most of the attributes that developers have been familiarized within Java. On top of that, we can also rely on Kotlin’s sophisticated function implementation and Functional Programming to orchestrate complex application programming logic.  


Syntax (code readability)

With some minor syntactic differences and conciseness thanks to data classes, smart casts, type interface, etc., Kotlin code reads quite similar to that of Java. You can avail syntactic advantages that allow you to develop the same programs with lesser coding. Hence, Kotlin syntax is less cumbersome for programmers to interpret, and suffice to say a program written in Kotlin takes less time to code than its Java counterpart.

E.g.: A simple calculator program in Kotlin that optimizes the same boilerplate code written in Java

fun calculate (a: Double, op: String, b: Double): Double {

       when (op) {

               "add" -> return a + b

               "subtract" -> return a - b

               "multiply" -> return a * b

               "divide" - > return a / b

               else -> throw Exception()



Function implementation

As an OOP language, Kotlin allows coders to declare functions locally (nested functions), or as member (class) functions or extension functions. One can also choose to declare functions outside of a class, as top-level functions.

Extension functions do not need classes themselves to extend the properties of a class, which helps prevent bloat in the size of a program; a very handy feature to have for modular, OOP app-building where various modules are coming together to constitute a multi-faceted application. Extensions also help inherit/extend properties from existing classes, types, and objects which omit the need to alter the source code.

Here’s a comparison of how an extension function utility is used in Java and Kotlin, side by side:


StringUtils.emojify(string: String);



This is also a prime example of Kotlin’s condensed syntax and performant compiler which directly interprets the extension function as a static function.

Kotlin’s Functional Programming attributes allow coders to declare higher-order functions. Kotlin employs first-class functions, which enable developers to pass functions as arguments or stored in variables or data structures. It needs to be noted that, passing a variable number of arguments through a function is also a possibility in Kotlin if you use the ‘vararg’ modifier, e.g.:

fun <T> asList(vararg ts: T): List<T> {

   val result = ArrayList<T>()

   for (t in ts) // ts is an Array


   return. result


Kotlin grants developers sophisticated use of higher-order functions by facilitating anonymous functions and lambda expressions.

Kotlin also helps developers circumvent stack overflows with the help of Tail Recursive functions. These functions help establish algorithms using loops instead of recursive functions. The ‘tailrec’ modifier the Kotlin compiler optimizes out the recursion and facilitates an efficient loop based version of the function instead.


Kotlin/Native uses the compiler technology LLMV to compile Kotlin sources into stand-alone binaries for multiple operating systems and CPU architectures like iOS, Linux, Windows, Mac, and Webassembly.

Kotlin’s compiler permits smart cast operators wherever required but does not explicitly require them in every case. When it comes to debugging, Kotlin’s sophisticated compiler detects errors at compile-time, instead of runtime, thus establishing a “fail-fast” principle. It performs checks that reduce the possibility of developers encountering runtime errors.

The Kotlin compiler also reduces code-heaviness in apps by utilizing sealed classes for the event-based logic used in contemporary Android programs. On a side-note, these sealed-classes are also useful for coding UIStates.  


Contrary to common misconceptions, Kotlin does not feature a separate ‘runtime’ like JRE. The Kotlin runtime, much like its error-handling capabilities, consists of a runtime class library. The runtime has to be bundled by the compiler with the compiled byte code. The ‘-include-runtime’ specifier grants self-contained programs runnable by including the Kotlin runtime library in it. Every version of Kotlin comprises compilers for JVM, JavaScript, and even native binaries for supported platforms. These compilers come into play when the developer compiles/runs the code.

Android currently uses ART which executes in both Dex bytecode format, as well as the predecessor Dalvik bytecode format. ART compiles the Kotlin code into Dex bytecode instead of JVM code like Kotlin’s compiler. ART supports Kotlin coded-legacy apps that were targeted for Dalvik, and overall improve app code performance with its AOT compilation, better install-time verification compared to Dalvik, and better garbage collection.

Error handling

Kotlin has a ’Throwable’, library class for exceptions that consists of messages, stacks trace, and an optional cause for every exception.

Kotlin’s codebase is built in ways that can help developers avoid error-prone practices. For instance, the in-built null references under unchecked exceptions which help prevent runtime errors, or the lack of checked exceptions which reduces the risk of compile-time errors, etc.

Memory Management

Kotlin possesses a memory management scheme that is quite similar to that of Java and even Swift for that matter. However, as opposed to Swift’s Automatic Reference Counting for garbage collection, Kotlin uses a tracing garbage collection procedure with CMS (Concurrent Mark-Sweep algorithm) for memory management. This memory management scheme is automated and in its latest iteration uses an automated reference counter that consists of a cycle collector for cyclical garbage.  


Build-cycle advantages

  1. Kotlin also offers code reusability thanks to its OOP capabilities.
  2. Kotlin’s interoperability allows you to also compile in multiple languages, side by side; this allows developers to use libraries written in other languages with ease. Thanks to Kotlin’s JVM compatibility, one can even rely on the beneficial features of Java OOP development too.    
  3. Does not have checked exceptions, like Java, which consumes development time as one needs to work around empty catch blocks and non-existent exceptions. Hence, app maintenance and crash frequencies are less recurrent.
  4. A less verbose syntax and other inherent qualities grant a faster time-to-market for Kotlin apps, in comparison to Java.
  5. Android KTX is divided into independent modules, where each module consists of one or more packages. Android KTX contains a single core module that provides Kotlin extensions for common framework APIs and several domain-specific extensions. Developers frequently use the Android KTX extensions which grant features such as extension functions

and properties, lambdas, named parameters, parameter default values

coroutines, etc.

Build security

Inbuilt null safety paves way for stable Android app builds. The Kotlin type system prevents developers from making null references, which is a huge step-up as with Kotlin a developer can safely declare null fields with and have the compiler handle it correctly.  

Kotlin’s use of immutable variables, collections, and classes also comes in handy in creating programs.


The scalability potential of your applications is endless when you code them with Kotlin. Developers use Kotlin’s coroutines to build server-side applications that scale to massive numbers of clients with modest hardware requirements.

Kotlin is directly endorsed by Google now, so you can easily scale your apps on Android, with complex but intuitive features and hope to consistently provide users a seamless, native UX.

Platforms supported

Kotlin Native allows us to develop applications for the iOS and Mac OS operating systems as well, besides Android and Windows. The best part about using Kotlin to build applications for various platforms is that it has a singular codebase. Developers have to write platform-specific code only where it is necessary.


Kotlin was built as a language for writing applications that target the JVM and Android environment; however, it has grown to support Android to Native iOS application migrations as well.

Most of the Android libraries today, such as AndroidX libraries, Android 9 libraries,  and the Android KTX library are coded in Kotlin. With decreasing support for Android Java APIs, developers must consider migrating to Android with Kotlin, rather than Java.

Migrating multiplatform Kotlin projects to other platforms is also not a challenge post-Kotlin ver. 1.6.0., and with the help of Gradle 6.0 and above.

Support community

Although Java is still the primary Android programming language, as endorsed by its proprietor, Google, Kotlin has also gained Google’s support as thousands of developers have thronged the Kotlin development ecosystem for modern Android app-builds. Kotlin takes little time to master for even absolute novices in Android development with the wealth of learning resources and courses available.

There is also a veritable number of free and premium IDEs, SDKs, and libraries available for Kotlin that are helping the language mature fast.

Type of applications

Kotlin finds preference from a growing sea of developers when it comes to Android app development, server-side scripting, web development, mobile app development, native app development, and even data science applications.

Kotlin is the development language behind approximately 60% of the applications on the Android Play Store, according to Google. Needless to say, Kotlin is a lot younger than Java in terms of maturity; But, it is still responsible for a diverse and commercially successful array of applications and web portals, such as Trello, Netflix, Pinterest, Slack, Tinder, Basecamp, Airbnb, and more.


As an Android app development language, Java is time-tested, while Kotlin opens the doors to more innovative vistas of programming. Java may have grown ‘clunkier’ and outdated in certain aspects where Kotlin does the trick with a few lines of code, but Java is still the bedrock of Android development

Hence, based on their use cases, both Java and Kotlin find equal footing in Android app development.


Java has a Verbose, syntax-heavy code that increases the risk of errors and program size. Unlike Kotlin, Java does not have data classes that can auto-generate boilerplate code like equals, hashCode, toString, getters/setters.  Consequently, development and deployment time for applications is longer, as well.

Kotlin has a precise and comparatively less, syntactically verbose codebase. As explained in the sections above, undercuts time consumption in every step, generating stable, ‘compact’ application code.

If time is a crucial factor and constrained, then Kotlin is the ideal pick over Java.


Java has several readily available Android app-architecture components available for your bespoke app development needs. Multi-threading, static members, wildcard types, singletons, and non-private fields in Java are a few advantages it holds over Kotlin when it comes to coding complex programming logic that does not strain hardware resources.

Kotlin addresses some drawbacks in Java with new features such as delegations, invariant arrays, late initializations, and type safety in lists and general code with the lack of raw types that can throw execution-time errors in apps. It features numerous virtues that make OOP-based app-building less time-consuming and facilitates complex, first-class Functional programming, alongside well-recognized OOP concepts. Kotlin’s in-built null safety feature for more stable, error-free programs. Co-routines assist coders with asynchronous code development, thereby increasing the efficiency of common tasks like database updates, network calls, etc.

Java and Kotlin are both good options technology-wise because of their merits and demerits. Businesses may choose either language based on how they meet the other resource parameters such as time, development skill required, and budget, in their specific requirement.

Development skill

Java syntax, though verbose, is one of the most popular high-level OOP languages to exist; every coder has a working knowledge of Java to a certain grade which enables them to inevitably fall back on Java for any Android application idea. It also means that Java, hands down, has the biggest support community for application developers.

Kotlin has a precise and comparatively less, syntactically verbose codebase which is easy to master for flawless developmental coding. But, despite its intuitiveness, Kotlin’s compiler is prone to complex errors. For example, smart casts may allow raw types as mentioned before, but these are not detected as errors at compile-time, but at execution time, leading to app crashes. Finding developers who can debug or develop error-free programs efficiently is difficult if you have time constraints.

Java is the ideal option in this use case if your developmental talent lacks the knowhow in end-to-end Kotlin software development.

Project Size

Finding developers who can readily produce development and maintenance solutions for your Kotlin app is difficult and costly. Also, even though Kotlin already has a widespread, multiplying support community, it is nowhere close to that of Java. As a result, Kotlin’s full-stack development cycle is not as hassle-free as one would like it to be for complex, multi-faceted projects.

Java’s maintenance (and development!) time is longer because despite familiarity there is more code to read through for developers. E.g.: checked exceptions in Java, where the compiler forces a function call to catch or re-throw an exception, resulting in empty catch blocks; these catch blocks consume time to track down and rectify.

However, that should not debunk the other merits of either of these languages., if your project size is small, with limited scope for feature scalability, then Kotlin is the ideal choice. That being said, with a sufficient budget, even with a larger project you may choose Kotlin and still hope for a good ROI; case in hand, Netflix. You can rely on Java provided you have a big budget to support a project of proportional size.


Java supports also Android Runtime (which honestly Kotlin does as well) as explained above, thus optimizing app code performance. In financial terms, this lessens your costs for developmental upskilling and app maintenance as any competent developer who has sufficient familiarity with Java can look up to its support community for troubleshooting. It also reduces your costs to use Java tools, as Java’s IDE and tooling support is unmatched. There are IDEs for Java built by the developers of Kotlin themselves!

Troubleshooting Kotlin code bugs can be treacherous and time-consuming at times for the plain reason that it is still a developing language and developers do not always have readily-available answers to Kotlin code-problems as Java.

If the budget supports your project size then you should pick Java, no matter the size of the project or its scalability prospects. If that does not hold good, then Kotlin works just fine.

In today’s competitive app development market we cannot abandon either Kotlin or Java entirely. As a versatile team of Progressive Web App developers for various desktop and mobile platforms including Android, at Tempest House we leverage the interoperability between Java VM bytecode and Kotlin VM bytecode, to help businesses update their legacy applications and endow them with trendier features leveraging interdisciplinary technologies. However, we are also specialized in full-stack, bespoke Android app development in pure Java or Kotlin.

Our software engineering network is built with experts from over 10 different nations, each boasting 10+ years of experience in cross-disciplinary tech verticals. Thanks to the cumulative and collaborative experience of our software specialists, we specialize in producing tailored, full-stack Android app solutions for established, multi-national businesses and start-ups alike.

Schedule a free consulting call with one of our experts to find out more about how our competitively-priced Android app development services can help you bring your app ideas to life.