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Choosing between Kotlin and Java depends less on which language is “better” and more on your project, team, and long-term goals. Kotlin is typically the better choice for modern Android development and teams prioritising concise, expressive code, while Java remains a strong option for large-scale enterprise systems, legacy environments, and stability-focused teams. In practice, many organisations adopt a hybrid approach, using Kotlin alongside Java to modernise gradually without disrupting existing systems.
This article seeks to explain the main differences between both programming languages. Afterward, we'll discuss which one is better and highlight the main reasons.
In short:
Java is a mature, object-oriented programming language that has been around since 1995. It is an open-source, general-purpose, object-oriented programming language. It’s known for its portability ("write once, run anywhere"), extensive libraries, and widespread adoption across enterprise and Android development. In addition, since it is compiled to bytecode, it can run on any Java Virtual Machine (JVM).
Java remains a cornerstone of enterprise software, supported by long-term releases such as Java 21 (LTS), which provide stability, performance improvements, and long-term support for large-scale systems. Many organisations rely on dedicated Java development services to build and maintain scalable applications.
Kotlin is a modern programming language developed by JetBrains, officially supported by Google for Android development since 2017. It's an open-source language that can also compile code to bytecode and run on Java Virtual Machine (JVM), enabling it to work on almost any platform. It’s designed to be concise, expressive, and interoperable with Java.
Kotlin is the preferred language for Android development, following Google’s Kotlin-first approach, which positions Kotlin as the primary language for building modern Android applications.
Kotlin and Java are not just competing languages—they dominate different parts of the software ecosystem.
Kotlin has become the leading language for Android development. Today, over 60% of professional Android developers use Kotlin, and more than 95% of the top 1,000 Android apps include Kotlin code.
This shift is largely driven by Google’s Kotlin-first approach and the language’s ability to reduce boilerplate and improve code safety. In fact, apps built with Kotlin have been shown to have up to 20% fewer crashes, largely due to improved null safety.
Kotlin adoption is also expanding beyond Android. According to JetBrains, Kotlin is widely used for both Android and server-side development, with a growing share of developers adopting it for backend systems and multiplatform projects.
Additionally, Kotlin Multiplatform adoption is accelerating, with usage increasing from 7% to 18% in just one year, highlighting growing confidence in Kotlin across platforms.
Java, however, remains dominant in enterprise environments. It is still one of the most demanded programming languages globally.
In enterprise systems, Java adoption can reach around 90%, reflecting its deep integration into legacy platforms, banking systems, and large-scale backend architectures.
Kotlin adoption in enterprise environments is growing but still comparatively lower. For example, internal adoption in large organisations can be gradual, some companies report adoption levels around 10–15% after several years of migration efforts.
Key takeaway:
Kotlin and Java both run on the Java Virtual Machine (JVM), compiling to the same bytecode, which means they share very similar runtime performance characteristics in most real-world applications.
Both Kotlin and Java are compiled into JVM bytecode before execution. This means that, from the JVM’s perspective, Kotlin and Java applications are largely indistinguishable at runtime.
As a result, Kotlin can use existing Java libraries, frameworks (such as Spring Boot), and tooling without compatibility issues.
The JVM uses Just-In-Time (JIT) compilation to optimise code during execution. This process analyses frequently executed code paths and compiles them into highly optimised machine code.
Because both Kotlin and Java compile to the same bytecode, they benefit equally from JVM optimisations such as:
In practice, this means that performance differences between Kotlin and Java are usually negligible in production environments.
Memory management for both Kotlin and Java is handled by the JVM’s garbage collector, which automatically manages object allocation and deallocation.
While Kotlin introduces some additional abstractions (such as higher-order functions and coroutines), these are designed to compile efficiently to JVM bytecode and typically do not introduce significant overhead.
Java, however, has a longer history of performance tuning in enterprise environments, which can make it slightly more predictable in highly optimised systems.
From a runtime and architectural perspective:
Kotlin and Java continue to evolve, and their latest versions reflect different priorities.
Kotlin 2.x focuses on improving developer productivity, faster compilation, and modern language features designed for readability and maintainability.
Java 21, a long-term support (LTS) release, focuses on performance, stability, and scalability. It introduces features such as virtual threads, which significantly improve how Java handles concurrency at scale.
In practice:
Kotlin and Java are often compared because they share the same runtime, the Java Virtual Machine (JVM), and are fully interoperable, meaning they can be used together within the same codebase. This makes them direct alternatives for many of the same use cases, particularly in backend development and Android applications.
Java remains one of the most widely used programming languages globally, with decades of adoption across enterprise systems, large-scale platforms, and long-lived applications. Kotlin, while newer, has rapidly gained traction, especially in Android development, thanks to its modern syntax, reduced boilerplate, and developer-friendly features.
Google officially announced a Kotlin-first approach for Android, positioning it as the preferred language for modern Android development. As a result, Kotlin has seen strong adoption growth, particularly among teams building new applications or modernising existing Java-based systems.
Kotlin’s dominance in Android is clear. Today, over 95% of the top Android apps include Kotlin code, and the majority of professional Android developers use it as their primary language.
Now that we have a bit of context, you might wonder how Kotlin's growth impacts Java. Will Kotlin replace it? The answer is not that simple. There are a lot of mixed opinions on this subject. To understand both sides of the debates, let's first take a close look at their differences.
Kotlin has built-in null safety, which helps prevent null pointer exceptions at compile time. Java can handle null values reliably too, but it usually requires more manual checks and defensive coding.
import kotlinx.coroutines.*
fun main() = runBlocking {
val result = async {
delay(1000)
"Data loaded"
}
println(result.await())
}public class NullHandlingExample {
public static String getUserName(String name) {
return name != null ? name.toUpperCase() : "UNKNOWN";
}
}
Kotlin offers a more concise and expressive syntax. For example, Kotlin eliminates boilerplate getters/setters and supports type inference. Java has made improvements in recent versions, but still tends to be more verbose.
About data objects, Kotlin data classes automatically generate useful methods such as toString(), equals(), hashCode(), and copy(). In Java, developers usually need to write these methods manually unless they rely on records or third-party libraries.
data class User(val name: String, val age: Int)
fun main() {
val user = User("Alice", 28)
println(user)
}
public class User {
private final String name;
private final int age;
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "User{name='" + name + "', age=" + age + "}";
}
}
Kotlin uses coroutines to simplify asynchronous programming, making async code easier to read and maintain. Java supports async workflows through tools like CompletableFuture, but the syntax is often more verbose.
import kotlinx.coroutines.*
fun main() = runBlocking {
val result = async {
delay(1000)
"Data loaded"
}
println(result.await())
}
import java.util.concurrent.CompletableFuture;
public class AsyncExample {
public static void main(String[] args) {
CompletableFuture<String> result = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Data loaded";
});
System.out.println(result.join());
}
}
Kotlin’s type inference has improved with the K2 compiler, allowing for smarter deductions and cleaner code. Java supports limited type inference, mostly within local variables (var keyword).
Kotlin provides coroutines for asynchronous programming, which are lightweight and easy to use. Java 21 introduced Virtual Threads, providing a new way to handle concurrency more efficiently, narrowing the gap between the two languages.
Kotlin’s compiler smartly handles type casting, and Kotlin 2.0 has made this even more efficient. Java requires explicit casting, which can lead to more verbose code.
Java forces developers to handle exceptions using try-catch blocks or by declaring them with throws. Kotlin removes checked exceptions, offering cleaner code at the cost of potentially missing error handling.
Kotlin supports extension functions, which let developers add new behaviour to existing classes without modifying their source code. Java does not have native extension functions, so similar behaviour is usually implemented with utility classes and static methods.
fun String.addGreeting(): String {
return "Hello, $this"
}
fun main() {
println("Alice".addGreeting())
}
public class ExtensionPatternExample {
public static String addGreeting(String value) {
return "Hello, " + value;
}
public static void main(String[] args) {
System.out.println(addGreeting("Alice"));
}
}
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Kotlin supports scripting and building domain-specific languages (DSLs) more effectively than Java, making it a favourite for configuration and build scripts.
Both languages are interoperable. Kotlin is fully compatible with Java and can call and be called from Java code. Interoperability is more seamless with recent improvements in both toolchains.
Kotlin continues to gain first-class support in JetBrains IntelliJ IDEA and Android Studio. Java also benefits from strong support in major IDEs and recent enhancements to debugging and profiling tools.
Java has a massive legacy ecosystem and is dominant in enterprise environments. Kotlin is growing rapidly, especially among startups and mobile developers. Both languages have strong communities and frequent updates.
Java is generally the better starting point for beginners due to its simplicity, widespread use, and strong focus on foundational programming concepts, while Kotlin is ideal as a second step for modern development.
Java has been taught for decades and is widely used in universities, bootcamps, and enterprise environments, making it one of the most accessible entry points into programming. It provides a clear introduction to object-oriented principles that are still relevant across many languages and systems.
Kotlin, on the other hand, is more concise and modern, but introduces additional concepts such as null safety and functional patterns that can feel less intuitive for complete beginners.
As a general recommendation, start with Java to build a solid foundation, then transition to Kotlin to improve productivity and work on modern applications—especially Android.
If your goal is specifically Android development, starting directly with Kotlin is also a valid and increasingly common approach.
Yes, Kotlin and Java are fully interoperable, which means they can be used together seamlessly within the same project.
Both languages run on the Java Virtual Machine (JVM), allowing Kotlin code to call Java code and vice versa without significant limitations. This makes it possible to introduce Kotlin gradually into existing Java systems.
The main trade-off is organisational rather than technical. Mixing languages can introduce some complexity in terms of code consistency, team conventions, and project structure if not managed carefully.
In practice, the best approach is often to use Kotlin for new features while maintaining stable parts of the system in Java. This allows teams to modernise incrementally without disrupting existing functionality.
To make this approach effective, it’s important to keep shared models consistent, align coding standards across the team, and avoid unnecessary duplication between languages.
The safest way to migrate from Java to Kotlin is incrementally, starting with new features, validating interoperability, and avoiding full rewrites.
1. Begin by assessing your codebase to identify which parts are stable and which are actively being developed. This helps prioritise where Kotlin can be introduced with the least risk.
2. Start by writing new features or modules in Kotlin while keeping the existing Java code intact. Thanks to full interoperability, both languages can coexist without major friction.
3. Introduce Kotlin gradually rather than attempting a full migration. Large-scale rewrites often introduce unnecessary risk and slow down delivery.
4. Ensure your team is aligned on Kotlin best practices and that your build tools (such as Gradle or Maven) are properly configured to support Kotlin.
5. Refactor Java code into Kotlin opportunistically, focusing on areas that are already being updated or maintained.
6. Throughout the process, test continuously to ensure compatibility between Kotlin and Java components, and monitor performance to avoid regressions.
7. Finally, define clear guidelines for when to use Kotlin versus Java going forward, so the codebase evolves in a consistent and maintainable way.
In one typical backend modernisation scenario, a team migrated part of a Spring Boot service from Java to Kotlin to improve developer productivity and reduce code complexity.
The project involved a mid-sized service responsible for handling API requests and business logic, originally written entirely in Java. Rather than rewriting the entire system, the team introduced Kotlin incrementally, starting with new features and gradually refactoring existing components.
This approach is supported by Kotlin’s design: the language is fully interoperable with Java, allowing both to coexist and interact seamlessly within the same codebase.
These improvements align with Kotlin’s design goals: reducing boilerplate and improving safety compared to Java, as highlighted in the official language comparison.
The team did not observe any significant runtime performance differences. This is expected because both Kotlin and Java:
Kotlin’s JVM-based architecture ensures compatibility with existing Java systems while enabling gradual adoption without performance penalties.
The team followed a gradual strategy:
This approach reflects real-world practices observed in Android and JVM ecosystems, where Kotlin adoption often happens alongside existing Java codebases rather than replacing them entirely.
This type of migration is common in product modernisation projects delivered through product development services, where teams balance innovation with stability.
Incremental adoption of Kotlin in a Java-based backend can deliver measurable improvements in:
—all without introducing significant risk or requiring a full rewrite.
In practice, choosing between Kotlin and Java is rarely about the language alone—it’s about delivery speed, system constraints, team capability, and long-term maintainability. Based on real-world product development and modernisation projects, here’s how we approach the decision.
We typically recommend Kotlin for new products and modern architectures, especially when speed and developer experience are priorities.
In these cases, Kotlin helps teams ship faster with fewer bugs and cleaner code
Java remains the right choice in environments where stability, predictability, and scale are more important than syntactic improvements.
In these cases, Java reduces risk and ensures continuity and operational stability
In reality, the most effective approach is often not choosing one over the other.
We frequently introduce Kotlin into existing Java systems incrementally:
This approach balances innovation with stability, avoiding the cost and risk of full migrations
If you need a quick rule of thumb:
In many real-world projects, teams do not replace Java entirely. Instead, they introduce Kotlin incrementally.
A common pattern is:
This approach allows teams to modernise their stack without disrupting production systems, while still benefiting from Kotlin’s improved developer experience.
Kotlin vs Java, which is better? Both have their strengths. Kotlin is more modern, with concise syntax and null safety, and is officially supported by Google for Android development. Java, however, has a larger ecosystem, mature tools and libraries. "Better" depends on your project needs.
But first and foremost, despite their differences, both Java and Kotlin compile to bytecode. Therefore, you can easily call Kotlin code to Java or the other way around, which allows both languages to be used in the same development project.
As we have explained, Kotlin does offer numerous advantages regarding Android development, but is Kotlin better than Java? Well, it does have some benefits over its competitor:
Nonetheless, let's not forget that Java also has its own benefits:
Now that we have highlighted each language's benefits, it is even harder to choose between Kotlin and Java, right? Well, let's try to take a pragmatic look.
Kotlin has been emerging as the new Android language. Its success comes from the fact that it introduces vital features that are making developers' life a lot easier, such as extension functions, lambda expressions and high-order functions, coroutines, and no NullPointerExceptions.
These are just some of the features that make it safe to affirm that, yes, Kotlin is better than Java for Android development and is likely to dominate in the future.
Is Kotlin Replacing Java? Everything seems to be moving toward Kotlin, and the new development tools that are rising know it! However, Java still has a lot of value and should not be neglected.
For general-purpose programming, Java still got it. Even for Android development, it remains an excellent language, and it is entirely understandable why some developers choose it.
Truth be told, it also depends on what languages the development team is using and which programming language feels more comfortable. These are all valid concerns. Plus, Java has been one of the most popular languages for years, so the chances of being entirely replaced soon are low.
Kotlin and Java are closer than ever in terms of capabilities, thanks to continuous improvements. If you value modern syntax, concise code, and cross-platform capabilities, Kotlin is a strong choice. For enterprise-grade scalability and long-term stability, Java remains a solid option.
Choosing between them comes down to your project requirements, team expertise, and platform goals.
Still not sure which language is right for your next project? Get in touch with our expert development team. We’ll help you evaluate your needs, build a tailored tech stack, and bring your ideas to life with the right tools from day one.
Kotlin is generally better for modern development, especially Android, due to its concise syntax and built-in safety features, while Java remains stronger for large-scale enterprise systems.
Kotlin reduces boilerplate code and prevents common errors like null pointer exceptions, whereas Java offers long-term stability and a larger ecosystem.
If you are new to programming, start with Kotlin; if you want broader career flexibility, start with Java.
Kotlin is easier to learn and more concise, while Java provides a strong foundation and is still widely used across enterprise systems.
Kotlin is Google’s recommended language for Android because it improves productivity, safety, and code readability.
It integrates seamlessly with existing Java code and supports modern features like coroutines for asynchronous programming.
Kotlin is unlikely to fully replace Java but is increasingly used alongside it in modern JVM development.
Most organisations adopt Kotlin gradually while maintaining existing Java codebases.
Kotlin and Java have similar performance because both run on the JVM, but Kotlin can improve developer productivity.
In some cases, Kotlin’s features (like inline functions) can optimise performance, but differences are usually minimal.
Yes, Kotlin and Java are fully interoperable and can be used in the same project without issues.
This makes it easy to migrate Java applications to Kotlin incrementally.
Yes, Java remains highly relevant, especially in enterprise systems, backend services, and large-scale applications.
It continues to be one of the most widely used programming languages globally.
Kotlin offers less boilerplate code, built-in null safety, and modern language features that improve developer efficiency.
It also supports functional programming patterns and simplifies asynchronous code with coroutines.
Java provides a mature ecosystem, long-term stability, and a larger pool of developers.
It is often preferred for enterprise applications where reliability and long-term support are critical.
Choose Kotlin for Android apps, modern JVM projects, and teams prioritising speed and maintainability.
It is particularly effective for new projects and gradual modernisation of Java systems.
Choose Java for large, legacy systems, enterprise environments, and teams that require long-term stability and scalability.
It is also a safer choice when working with older frameworks or large development teams.
Kotlin is generally easier to maintain due to its concise syntax and reduced risk of common errors.
However, maintainability also depends on team familiarity and project complexity.
Marketing intern with a particular interest in technology and research. In my free time, I play volleyball and spoil my dog as much as possible.
Software developer with a big curiosity about technology and how it impacts our life. Love for sports, music, and learning!
Alexandra Mendes is a Senior Growth Specialist at Imaginary Cloud with 3+ years of experience writing about software development, AI, and digital transformation. After completing a frontend development course, Alexandra picked up some hands-on coding skills and now works closely with technical teams. Passionate about how new technologies shape business and society, Alexandra enjoys turning complex topics into clear, helpful content for decision-makers.
CEO @ Imaginary Cloud and co-author of the Product Design Process book. I enjoy food, wine, and Krav Maga (not necessarily in this order).
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