Kotlin vs. Java: What To Choose for an Android App?

To create Android apps, developers use either Java or Kotlin. When starting a new mobile project, you may wonder, “Should I build it on Java or use Kotlin instead?”

For me, as for the Android developer, the answer is obvious. For you, as for a person without a background in coding, the choice between those languages might not be so easy. 

To draw you an overall picture, let me give you an example. When choosing between the old but gold Honda Accord and Tesla Model S, what would you select? I doubt you’ll choose the first option. Similarly, the answer for “Java vs. Kotlin-question” is clear to developers, but not to all C-levels and decision-makers.

I have written this article to give you a clue why most developers use Kotlin for new Android projects, and when Java code can still exist in your mobile application. 

But first, let’s take a closer look at Java, Kotlin, and their main differences.

What is Java?

Java is an object-oriented programming language, named after an island in the Indian ocean. 

The first Java release was 25 years ago, in 1995. Since then, Java has become widely used in the community of developers. And there are several reasons for its popularity:  

  • Simplicity (its code looks like C/C++) 
  • Wide range of applications (from mobile applications to database connectivity)
  • Open-source libraries (logging, JSON parsing, unit testing, etc.)


The following businesses are using Java in their products:

  • Netflix uses Java for open-source tools and in the majority of the services within its architecture
  • Uber leverages Java for developing Map Services, integrating external technologies, and analytics tools.
  • Airbnb uses the language for their backend services in combination with the Dropwizard web service framework 
  • Google relies on Java for servers and the user interface

Java code example

Here is how Java Hello world code looks: 

// Your First Program

class HelloWorld {

    public static void main(String[] args) {

        System.out.println(“Hello, World!”); 



Now, let’s find out why mobile app developers like and don’t like Java at the same time. 

What developers like about Java 

I think that the Java language is not so bad for the following reasons: 

Platform agnostic. I can use Java, not only for coding Android apps but also for web and cross-platform applications. 

Established community. When I have an issue with code, I’ll find help in GitHub and Stack Overflow Java online communities. 

Flexibility. I can build Java applications on Java Virtual Machine (JVM) and a browser window.

Code reusability. I can use code from one project in multiple apps that need it, which slightly reduces the development time. 

What developers don’t like about Java

Developers almost hate Java. Really. Reddit’s thread “Why does everyone hate Java” includes 1700+ answers to this question. I find Java inconvenient for the following reasons:

Repetitive syntax. The code is drowned out in type declarations, temporary classes, and factories, which distracts me from fixing the actual problem.

Large code. When I write highly modular code with small cohesive methods, the code loses its readability and makes unit testing and code reuse extremely complicated. 

Memory issues. The memory management happens through garbage collection, which slows down an app’s work. 

Developers have used Java as an initial coding language for Android applications since the Android launch in 2008. Things changed in 2017, when Google, the official provider of Android Studio, announced Java is no longer a preferred language for developing apps. But what did Google recommend for creating Android applications instead of Java? Well, that’s Kotlin. 


What is Kotlin?

Kotlin is a cross-platform statically typed programming language with open source code. The first release of Kotlin was in 2011 by JetBrains s.r.o., a Czech software development team. 

In 2017, Kotlin became the official language for developing Android apps, announced at Google’s annual developer conference. 

It is 100% interoperable with Java code. The JVM version of Kotlin’s standard library depends on Class Library written in Java. But, thanks to type inference, Kotlin syntax is more concise, which makes Kotlin the fourth most enjoyable language to use, says The annual Stack Overflow survey

java vs kotlin

The following companies use Kotlin in their products already:

  • Gradle applies Kotlin for writing build scripts 
  • Atlassian made an Android version of Trello in Kotlin
  • Uber leveraged Kotlin for Android passenger and driver apps 
  • Pinterest has a Kotlin-made Android mobile application

Kotlin code example

One example of the Hello world Kotlin program looks like this:  

// Hello World Program

fun main(args : Array) {

    println(“Hello, World!”)

What developers like about Kotlin 

I find Kotlin the best language for Android app development due to: 

Less code. When I write code, I don’t need to create constructors for object initialization, classes to hold data, update, and retrieve values for declared fields. As a result, Kotlin code is 10%-20% shorter than Java code, which speeds up the development and deployment processes.

Java code vs Kotlin code


Easy to maintain. Since I write less code, I make fewer mistakes and my code has fewer bugs. Less code also means lower app maintenance costs. 

Simple in use. Kotlin eliminates Java-specific challenges, such as NullPointerException, and provides access to all frameworks and libraries written in Java for building clear and concise code.

Android Studio support. I use both Java and Kotlin code in the same project thanks to extended support and adaptation tools from Android Studio.


What developers don’t like about Kotlin 

Like everything in this world, Kotlin isn’t perfect. I find Kotlin adoption challenging for the following reasons: 

Steep education path. Kotlin’s syntax is different from other programming languages, which complicates its adoption. It also means that hiring Kotlin developers requires more time. 

Young community. In some cases, I can’t find answers in online community groups dedicated to Kotlin. But, I hope developers will solve this issue by contributing to Kotlin projects on GitHub and participating in issue discussions in StackOverflow

Now, let’s compare how Java is different from Kotlin in terms of functionality.


Kotlin vs. Java: the programming languages comparison table

In the table below, I included a detailed comparison of Java and Kotlin programming languages.  




Null Safe

Includes a NullPointerExceptions that raises a null pointer exception when accessing an object reference with a null value.  

Allows assigning null values to any variables/objects. 

Extension Functions

Requires creating a new class and inheriting the parent class, which means new functionality isn’t available. 

Allows creating extended functions by prefixing the name of a class to the name of the new function.

Coroutines Support

Blocks a corresponding thread during a long-running network I/0 and CPU Intensive operations. 

Includes coroutines support that suspends execution without blocking threads while executing long-running intensive operations.

Checked exceptions

Includes checked exceptions that declare and catch exceptions in code, which leads to a code with good error handling.

Doesn’t include checked exceptions. 

Data classes

Requires defining constructors, variables to store data, set methods, etc.

Declares a class with the keyword “data” in the class definition. Constructors, getter, and setter methods for different fields are created automatically.  

Smart casts

Requires checking the type of variables and casting according to an operation.

Includes smart casts for handling casting checks of immutable values and performing implicit casting.

Type inference

Requires specifying each variables’ type explicitly.

Specifies the variable type explicitly based on the assignment it handles.

Functional Programming

Provides functional programming support to only a subset of Java 8 features

Includes useful methods such as lambda, operator overloading, higher-order functions, etc.


With that being said, developers find Kotlin a far more convenient programming language. Its syntax doesn’t require us to repeat the same code when writing a new one. Thus, the “Java vs. Kotlin” question hasn’t arisen in the developer community in recent years. But, mobile app development isn’t that simple in practice. 

Before suggesting the relevant coding language for your project, I need to learn more about your business needs, expectations, and project goals. Moreover, there are even cases when I’ll recommend Java as the best option. 

To understand why mobile app development isn’t black and white, check out several examples from my experience. 

Related reading

How to Outsource App Development Without Failing

How The APP Solutions team works: Cooperation Models and Development Phases

The Discovery Phase with The APP Solutions

Java vs. Kotlin: What programming language an Android developer recommends

You’ll need an Android developer in several cases – to build Android applications from the ground up or add more advanced functionality to an existing application. Depending on the business case, the answer to the question “Java vs Kotlin?” varies. 

Developing an Android application from scratch

Before recommending the best programming language for new Android applications, the first thing I do is clarifying project deadlines, in-house dev team composition, and the budget. 

Tight deadlines, limited budget, and a small development team without previous experience in Kotlin are signs that you need to start your project with Java. From a business perspective, Android app development will cost you less. Since most mobile developers know Java, they can start the project at once. At the same time, you save time and budget on hiring Kotlin-experienced programmers. 

But, in the case of having enough time before the project launch, extra budget, and time for hiring additional developers, I recommend using Kotlin. 


Developing an Android application with pre-coded Java features

Some clients ask us to use existing Java algorithms, features, and plugins for their projects. At the same time, they want the code to be written on Kotlin but have no budget for re-building Java functionality. 

In this case, I recommend starting your project with Kotlin, then integrating Java pre-coded app functionality. This approach works because Kotlin is compiled with Java bytecode and JVM (Java Virtual Machine). 

To call existing Java code from Kotlin, developers use the following command: 

import java.util.*        

fun demo(source: List) {

    val list = ArrayList()

    // ‘for’-loops work for Java collections:

    for (item in source) {



    // Operator conventions work as well:

    for (i in 0..source.size – 1) {

        list[i] = source[i] // get and set are called




Adding new functionality into an existing Android app 

If your application was launched before 2017, I’m 99.99% sure it is written in Java. Now, you might need to integrate new business functionality. So, you’ll face the dilemma – to hire Android developers to re-write the app with Kotlin language or  integrate new functionality powered by Java? In both cases, the right answer is “no.” 

As I mentioned earlier, Java and Kotlin codes work together. Thus, re-building your application with Kotlin to receive a 100% Kotlin-written app doesn’t make any sense. For adding new functionality, I suggest using Kotlin, since there are many examples of both programming languages co-existing in one mobile application. 

One example is Passport Scan, the application we developed to streamline hotel check-in. The client challenged us with integrating a web application into an existing hotel management system, made with Java. 

We began building the core features using Java. But soon, we switched to Kotlin for adding the new app’s functionality. Learn more about the project by reading the Passport Scan case study

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Kotlin vs Java: What is the best language for Android app developers

Kotlin programming language addresses Java’s weak points – in syntax and memory usage, as well as other imperfections. And Kotlin is doing it well. The growing community of Kotlin developers proves that when a developer learns Kotlin, one will never write on Java again. 


Kotlin-built projects take less time to code, require fewer bugs to fix, and cost less, compared with Java applications. In contrast, developers can write a new mobile application in the Java language as an exception to the rule. 

If you have an idea for a Kotlin project and are looking for well-performing developers, drop us several lines. Let us know your idea, and we’ll figure out how we can be useful. 

Android App Development Cost

Did you know that iOS is going to disappear from the Asian market anytime soon?

Android apps become more popular in Asian market

Despite the enormous number of Apple gadgets throughout Asia, users here differ a lot from Americans – loyal lovers of i-devices. The trend is decreasing with iPhones – from 72% of all gadgets in 2012 to 50% in 2015.

Asian citizens got used to seeing technologies changing rapidly and they observe a lot more interesting technologies around than Apple. They also tend to prefer phablets for multiple purposes. Apple is not something special for them anymore, not to mention, it’s much more expensive than a huge variety of Android-charged gadgets.

Why ios apps become less popular

But anyway, it’s not the objective of our discussion today. Just to let you know that picking Android for mobile app development is the right choice. What’s more, Google Play Store is coming back to China this year, not to mention – it dominates in the Asian market even now.

Google Play returned to China in 2016

If you ask me, how much would it cost, even roughly, to build an average Android app, the answer would be – I have no clue really. That’s why I’ve been digging for precious bits of info to put together everything that builds up the price of a typical Android app. So here is a checklist of what you’ll know after reading the article:

  • what’s the current situation with Android apps globally;
  • peculiarities of Android mobile app development;
  • what features are trendy in Android apps among mobile application developers;
  • factors that influence your Android app’s price;
  • and finally, elements that build up the final cost of your mobile application.

I’m positive that you’ll become true experts of the Android apps world and will be able to calculate rough budgets for your future Android app projects. So let’s dive right into it!

SEE ALSO: How Business Applies Sentiment Analysis

What’s the hype about Android apps

There basically is a range of reasons why Android apps are more beneficial than iOS ones. Let me just leave one figure here for a start:

Android apps become more popular

The following features make the Android app more profitable to build:

  1. Java – this powerful coding language is a universal tool, which makes Android mobile applications highly portable to other operating systems such as Ubuntu, Symbian, and Blackberry. This can also become a deciding success factor of, say, a small startup, short on budget;
  2. Availability – apps published in Google Play Store are ready to download in a couple of hours after their launch unlike iOS apps (can be previewed for weeks before approval). The same with updated versions – they can be uploaded multiple times a day in response to feedback or complaints. Another benefit is the ability to publish a beta version of the app and provide access to a limited number of testers. That’s a cool and dynamic way to improve an app on the initial stage and then release it all polished and complete to a wide audience;
  3. Favorable entry-level – as far as iOS is a kinda closed network, it always requires more permissions to pass, payments to submit, and all that jazz. For Android it’s more user-friendly and easier: you can build an Android app on Mac, Linux, or Windows, whereas iOS apps – on Mac only; to register as a developer – one time $25-payment for Android vs monthly $99 for iOS;
  4. Profitability – currently Android apps become as profitable as iOS ones (even more rewarding in some cases), despite existing prejudice that iOS is used by richer, more open to paying, users. And again, thriving market share is the reason for that – almost 2 billion devices with the Android engine on hand for the year of 2015, according to Statista.

CHECK OUT MORE: IOS vs Android app development

Android in-app trends – what features to rock

Mobile technologies skyrocket on a daily basis and fresh trends continue appearing in the apps enhancing the user experience, productivity, and reliability of the app.

More security

Security is something taken for granted and absolutely expected by users. That’s why this aspect is given much attention recently and for a good reason. The thing is that for Android hacking issue is very actual and there are multiple cases still registered.

Want it or not, companies pay attention to this aspect religiously, coz alternatively, it can lead to a significant loss of the business.

A convincing example is online transactions. As they are getting more and more use within mobile applications, Android is working out powerful security solutions to ensure the full defense of personal user data.

Latest solutions allow building separate business environments for applications in order to protect any important data. This is expected to grow the number of enterprises adopting this OS starting from 2016.

Less time for development

Despite the well-known fact that Android apps take more time to be built (details will be broken down further in the article), the overall trend is still about shortening the time for building. The reason for that is shifting to a simple, clean design and interface of the application. “UX goes first” is trending and became a major focus for developers. And this trend is well-known mostly for its’ simplicity and minimalism.

READ ALSO: How Long Does it Take to Develop an iOS or Android Mobile App

Businesses want their apps built

Most companies already do their businesses online. As the majority of people spend most of their time on the phone, corporations must adapt to that swiftly. Enterprises decide to build specific commercial applications to stay in touch with their customers, not to mention, they also enhance consumer’s experience within the company. A positive and effortless user experience always equals loyalty, right?


Multiple surveys confirm that by the year 2018 smartphone payments will reach the point of almost $ 120 billion internationally. And it will be more than 50% of all online transactions. These figures speak for themselves. Just implement this feature and make your customers pay in a matter of clicks.

Assimilation of wearables

Smartwatches, smart bracelets, fitness trackers. More and more simple people change their conventional watches to some smart accessories. Companies integrate them to increase business productivity.

The best part is that Google provides a range of guidelines for Android Wear software and a lot of manufacturers implement it for their gadgets gratefully. This only means that most Android users will get some sort of smart wearable device sooner or later. And you wanna be armed for that.

What it takes to build an edgy Android app

Now that you know the Android app is a good deal, it’s time to outline the major peculiarities of the Android app development process. This will also influence the price of the application at the end of the day.

One prime statement for Android app development is that it usually would cost you somewhat more expensive than one for iOS. Let me unpack what’s so special about Android mobile development, which leads to a longer time to implement an application compared to the iOS one.

Number of lines

Yes, as easy as that. According to our analysis of QuePro and SpotNews Android apps, built by our team, it takes about 40% more code to complete an Android app than the iOS version. It’s not necessarily all hand-written code, part of it is auto-generated, but still, developers read it, debug and maintain.


[The App Solutions Project for All Square]

By the way, a trendy “clean architecture” requires even more lines of code because of the highly-structured coding approach.

Total of hours

Obviously, such a large difference in the volume of development work results in increased working hours for them. And it’s almost the same difference – up to 30% more time compared to iOS development hours.

Slower emulators

A significant factor that slows down the rhythm of Android development is the operational speed of Android emulators – they seem to be quite crawling against iOS emulators and you can’t fight it yet.

High fragmentation

Have you ever tried to calculate the number of all Android-charged gadgets?

Correct, it’s getting closer and closer to a range of impossible tasks. Whereas, iOS devices are on everybody’s A-list. And the range is quite thin. So again, it takes much more effort and time to test and fix issues for every screen.

What about all versions of Android operating nowadays in the global market? About 50% of iPhone owners adopted the latest version of iOS in 4 days after its’ release, while Marshmallow 6.0 is run hardly on 1% of Android smartphones.

Android versions adoption

Android app development cost

Pricing model

Now we know that the cost of the app in most cases depends on the number of hours spent to build it. This is a scenario majority of app development companies usually follow – the so-called Time & Material payment model. This one is very flexible and you are able to make changes and improvements along the way, at the same time optimizing tasks for developers and reducing the cost for inconvenient features or tasks.

On the other hand, there is a Fixed Price model. Here you agree on the final product from the very beginning and it’s much more difficult to implement changes because the development process here works in a different way – not with short iterations, but just delivering a complete project on time.

Both of these schemes will result in different prices. Usually, fixed price tends to be higher as the development company adds various risk factors to it.

Dedicated team

Another important component that builds up the price of your app is members of the team. A little disclaimer here! These are not only mobile app developers, who are creating your product.

An ultimate list of professionals whom you need to craft and polish your application:

  • Project manager – a professional who heads the whole team, communicates with you as a client, suggests some handy technical solutions, joins up the squad, and assures of delivering the project on time;
  • Senior developer or architect – this is a leading developer and a person who creates the whole strategy of the upcoming app;
  • Android coder(s) – guys who are implementing your idea into a unique piece of software;
  • Designer(s) – these are wizards of UX/UI design, they make application user-friendly and appealing to watch and use;
  • QA Engineer(s) – people in charge of final testing and debugging application, making it go like clockwork;
  • Technical writer – a person who creates a script of the whole idea and implementation of the app: from logic to changing screens and functions of every button.

This looks much like a skeleton of the dream team you need to build an Android app. Depending on the complexity of the desired product, the number of people can vary, but virtually all functions are distributed among these experts.

Kind of application

Table-based app – simplest among applications. Enables you to display information, provide options and redirect to additional materials.

Database app – more complex ones, good to present a wider range of data. These are usually connected to various websites or any other online services and broadcast requested information from there, which makes them more complex to build.

Dynamic app – very similar to a previous type and differs only by not really connecting to outer resources, but extracting info from them with the help of API.

Gaming app – known as most complex to craft. They can vary by functionality and integrated technologies, at the same time they are the most costly among all applications.

Among other, minor, influential aspects might be the business model of your app (or simply how you’re going to earn money with your app) and the complexity of the design.

Now it’s time to go ahead and look for the best app developers to entrust your important task to. You might look for your people in various regions of the world and hourly rate will differ of course:

  • USA/Canada-based dev teams – $50 to $250/hour;
  • Western Europe – $30 to$170/hour;
  • Eastern Europe – $20 to $150/hour;
  • Australia – $50 to $150/hour;
  • India – $10 to $80/hour.

Once a choice on mobile application developers is done, you can discuss all functionality of the application and get a rough estimation of the required number of hours to build it. Afterward, you simply add all hours of your team and multiply these on the hourly rate!

Concluding thoughts

As you can see, Indian mobile app developers will charge you the least out of all regions’ representatives. Just make sure you check the portfolio of the particular squad along with looking through the entire reputation. After all, famous rumors around Indian development “story” going on for a reason.

Eastern European professionals are famous for their high professionalism together with moderate pricing, so they are worth considering for sure.

Australian and American app developers are paid the highest out of this range. No need to worry about the quality and all the procedures in this case.

Just a hint for you, guys, – these will be in most cases East Europeans relocated to the US or Australia sitting there 🙂

Now congrats! You got good food for thought on the subject of developing your baby! A cherry on top – you can invest in a project in parts, so it’s not crucial to have the whole budget from the very launch of the project.

Try our calculator to figure out the cost of Android app development.

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