From Java to Kotlin: The Evolution of Android App Development and What It Means for Business

Android development has changed more over the past few years than it might seem at first glance. If Java once felt like the obvious choice, today another name is heard more and more often — Kotlin.

At Google I/O 2019, Kotlin was announced as the “preferred language” for Android development. Since then, many teams have shifted their projects toward it, attracted by concise code, built-in safety features, and support for modern tools. At the same time, Java remains a solid foundation: millions of apps, enterprise systems, and entire ecosystems still rely on it.

But the reality is that Kotlin has already replaced Java as the primary language for Android. For businesses, this shift raises a different set of questions: why did Kotlin become the new standard, and what should you do if your product still relies on a large Java codebase that no longer meets Google Play’s requirements? That’s exactly what we’ll explore in this article.

What is Java

Java is one of the oldest and most influential programming languages, first released in 1995. For the Android ecosystem, it became the foundation: the first versions of applications and even the Android platform itself were built with Java. Thanks to its stability and the vast number of available libraries, Java remained the primary choice for mobile developers for a long time.

When the first Android smartphone was released in 2008, the entire SDK and most of the tools were based on Java. This ensured a low entry barrier: developers familiar with the language from web or enterprise systems could easily transition to mobile app development.

What is Kotlin

Kotlin is a modern programming language created by JetBrains and officially released in 2011. Its objective was to provide a safer, more concise, and more convenient variant of Java, but it provides complete interoperability with Java. In its initial development years, the language gained rapid attention from Android developers as it has simple syntax, support for functional programming, and null safety.

According to Android Developers, 67% of Android developers report that Kotlin has improved their productivity, allowing them to write less boilerplate code and focus more on building new features.

Google recognized Kotlin’s growing popularity in the community and the fact that it addressed many of Java’s shortcomings: excessive boilerplate, null-related errors, and challenges with asynchronous programming. In 2017, the company officially announced support for Kotlin on Android, and in 2019, it made Kotlin the “preferred language” for mobile development. This move solidified Kotlin’s status as the primary tool for building Android apps and accelerated its widespread adoption.

Difference Between Java and Kotlin in Android Development

To better understand how Java and Kotlin differ, and where one has an edge over the other, it’s worth looking at them through several key aspects. These include syntax style and coding convenience, the capabilities of functional programming, their approaches to null handling and type safety, as well as how each language manages concurrency, performance, and the richness of its ecosystem of tools.

Syntax: Style and Code Readability

One of the first differences developers notice when switching from Java to Kotlin is the syntax. Kotlin was designed to be more concise and expressive, allowing developers to write less code without losing readability. Java, on the other hand, remains more traditional and verbose, which can sometimes make it easier for beginners to learn but increases the amount of boilerplate code.

kotlin
fun main() {
    println("Hello World")
}

Kotlin: Hello World

java
public class Main {
    public static void main(String[] args) {
        System.out.println(“Hello, World!”); 
    }
}

Java: Hello World

For clarity, it’s also helpful to summarize the differences in syntax. The table below shows how the choice of language affects code conciseness, readability, and the overall developer experience.

Comparison of Kotlin and Java Syntax

Functional Programming: Capabilities

One of the things developers appreciate about Kotlin is how naturally it supports functional programming. Lambdas, extension functions, and handy collection operations like map, filter, or reduce are built right into the language. This makes the code feel cleaner and more expressive — you spend less time writing boilerplate and more time focusing on the actual logic of the app.

Java also supports functional programming, but it came much later — starting with Java 8 and the introduction of the Stream API. Streams and lambdas made Java code look more modern, but they’re still more verbose compared to Kotlin. And since many Android projects are tied to older Java versions, not everyone can even use these features in full.

For Android apps, the difference is easy to feel: Kotlin makes it simpler to write reactive, elegant code that’s easy to follow, while Java often sticks to a more step-by-step, imperative style that tends to grow heavier over time.

Null Safety and Type Safety

Among developers, there’s an inside joke: one of the most common error messages in Java is the NullPointerException. In simple terms, this happens when a program tries to work with missing data where it shouldn’t. For programmers it’s a familiar bug, but for users it often means app crashes and broken functionality. And for businesses, that translates into lost customer trust and extra costs for fixing issues.

Kotlin addresses this problem at the language level. It forces developers to account for cases where data might be missing and provides built-in mechanisms that reduce the likelihood of such errors during development. As a result, apps built with Kotlin tend to be more stable and require fewer fixes down the road.

Java, on the other hand, doesn’t have this kind of built-in protection. Developers must rely on manual checks or extensive testing, which increases the risk of bugs slipping through and raises maintenance costs.

For businesses, the takeaway is clear: Kotlin helps deliver more reliable applications that crash less often, keep users more satisfied, and reduce long-term support expenses.

Concurrency and Performance

For mobile apps, it’s critical that they run smoothly and don’t “freeze” while loading data, refreshing content, or handling other background tasks. This directly affects user convenience, satisfaction, and their willingness to keep using the product.

Kotlin offers a modern tool — coroutines, which allow background tasks to be executed efficiently without overloading the system. As a result, apps become more responsive, run more smoothly, and consume less battery — all of which are highly valuable for end users.

In Java, the same problems are solved with traditional multithreading or reactive libraries like RxJava. These solutions are reliable but usually require more resources and make software development more complex and costly.

From a business perspective, the difference is clear: using Kotlin’s coroutines helps build faster and more energy-efficient applications, improving customer satisfaction and reducing the risk of users abandoning the product.

Ecosystem and Tools

For businesses, it’s not only about which language developers use, but also what tools come with it. The ecosystem determines how quickly new features can be released, how much ongoing support will cost, and how easily the app can evolve in the future.

Kotlin provides access to modern tools that directly impact product quality. With Google’s backing and deep integration into new technologies like Jetpack Compose, it enables faster app releases and easier design updates. Built-in features such as coroutines make applications more responsive and battery-friendly, while reducing boilerplate code helps lower development costs.

Java, while still used in some enterprise systems due to its maturity and reliability, no longer sets the standard for Android projects. Instead, Kotlin offers the flexibility, modern features, and long-term maintainability that businesses need to stay competitive.

Kotlin vs Java: Pros and Cons

Earlier we looked in detail at the differences between Kotlin and Java — from syntax and data handling to performance and ecosystem. Now it’s time to sum up: each language has its own strengths and weaknesses that affect development speed, product reliability, and maintenance costs in different ways.

Pros and Cons of Kotlin

Pros:

• Concise syntax. Shorter, cleaner code means faster feature delivery and lower maintenance costs.
• Google support. New tools and technologies are primarily optimized for Kotlin.
• Modern capabilities. Coroutines, Jetpack Compose, and null safety improve app stability and quality. In addition, Kotlin allows developers to leverage advanced functional programming features with less effort.
• Compiler efficiency. The Kotlin compiler helps catch issues early, preventing crashes in production.

Cons:

• Requires additional training if the team has only worked with Java before.
• The legacy ecosystem is still dominated by Java, so integration may require extra resources — especially when combining existing Java and Kotlin code in the same project.

Pros and Cons of Java

Pros:

• Stability and reliability. Millions of apps and libraries have been built with Java.
• Large community. A massive base of web development and mobile solutions, along with ready-made libraries, minimizes risks.
• High compatibility. Java supports enterprise systems and integrations, making it a safe choice for long-term projects.

Cons:

• Verbose code increases development time and support costs.
• Modern Android tools are increasingly designed with Kotlin in mind, gradually reducing Java’s role in mobile development.

Why does Kotlin Replace Java? A Realistic View

Today, the question is no longer “if” Kotlin will replace Java in Android development — it already has. Google has made Kotlin the default choice, with all new SDKs, libraries, and frameworks optimized for it first. Jetpack Compose, Android Studio tooling, and Play Store requirements are all designed around Kotlin, which means Java-based projects inevitably face limitations and growing risks of obsolescence.

For product owners, the real challenge is different: what to do with existing Java codebases. Many enterprise and consumer applications still rely on extensive Java foundations that continue to function reliably. But keeping them “as is” is no longer an option. Google Play enforces regular updates to target newer SDK versions, and outdated Java dependencies can quickly make an app non-compliant or even removed from distribution.

Rewriting everything from scratch is rarely realistic due to costs and risks. Instead, businesses are turning to step-by-step migration strategies:

• introducing Kotlin for new features and modules,
• gradually replacing outdated libraries,
• modernizing the most critical parts of the app first.

This approach allows companies to stay aligned with Google’s ecosystem while avoiding downtime and spreading out investments over time.

The key takeaway: Kotlin has become the new standard for Android, while Java survives only as legacy. For businesses, the real decision is not whether to adopt Kotlin, but how and when to modernize existing Java applications to stay competitive and compliant.

SCAND: Expertise in Android Development

For today’s Android development, Kotlin has become the default standard, while Java mostly remains in legacy codebases. The key challenge for businesses is not choosing between the two, but finding the right strategy to modernize existing Java applications and align them with Google’s requirements.

That’s where expertise matters. At SCAND, we help companies assess their current projects and plan efficient migration paths — from introducing Kotlin in new modules to full-scale modernization.

For over 25 years, our team has been developing software and has extensive experience building Android applications in both Java and Kotlin. We support projects at every stage — from concept to long-term maintenance — helping businesses strike the right balance between stability and innovation.

We offer:

• Android application development of any complexity — from MVPs to large-scale enterprise solutions.
• Guidance in choosing the right technology stack based on your project’s goals and budget.
• Migration and gradual transition from Java to Kotlin with no business risks and preserved system stability.
• Long-term support and evolution of applications to keep your product relevant and competitive.

If you are looking for a reliable partner to modernize your Android application, get in touch with us — our Kotlin and Java developers will help you ensure your project stays compliant, up-to-date, and ready for future growth.