Java vs Kotlin: A Comprehensive Comparison for Developers

Java developers often switch to the newer programming language — Kotlin. In this article, we'll compare these two languages, understand why people choose "Java's child," and determine which language is best for different tasks!

First, we need to understand what Java and Kotlin are and why they are so popular. Let's start from the beginning!

What is Java?

Java is a versatile and powerful programming language that's been around since the mid-'90s.

Imagine it as a tool that allows you to create anything from mobile apps to large-scale enterprise systems. It's known for its "write once, run anywhere" philosophy, which means you can write Java code on one device, and it can run on any other device that has a Java Virtual Machine (JVM) without needing to be rewritten.

Java is like the reliable workhorse of the programming world — steady, dependable, and used in countless applications around the globe. From Android apps on your phone to complex banking systems, Java's everywhere, quietly running the show.

What is Kotlin?

Kotlin is a modern programming language that’s designed to be expressive and enjoyable. It's known for its concise syntax, which allows developers to write less code to accomplish more. This makes Kotlin both powerful and easy to read, offering a smooth development experience.

One of the things that makes Kotlin stand out is its safety features. For example, it helps prevent common programming errors, such as null pointer exceptions, by making nullability a core part of the language. You must be explicit when a variable can hold a null value, reducing the chances of unexpected application crashes.

Kotlin also supports object-oriented and functional programming styles, allowing developers to choose the best approach for their needs. Its interoperability with existing systems makes it an attractive option for building modern applications without completely rewriting existing codebases.

History and Evolution

Let’s take a look at the timeline that highlights the key moments in the competition between Kotlin and Java:

1. 1995 - Release of Java: Java was officially released by Sun Microsystems, revolutionizing software development with its "write once, run anywhere" philosophy;
2. 2003 - Release of Spring Framework: The Spring Framework was introduced, becoming one of the most popular frameworks for building enterprise-level applications in Java;
3. 2001 - Release of Hibernate: Hibernate, a powerful object-relational mapping (ORM) tool for Java, was released, simplifying database interactions in Java applications;
4. 2000s (Mid to Late) - Peak Popularity of Java: Java experienced widespread adoption, particularly in enterprise environments, solidifying its position as one of the most popular programming languages in the world;
5. 2011 - Release of Kotlin: Kotlin was introduced by JetBrains as a modern, concise, and safer alternative for Java developers;
6. 2020s (Early) - Peak Popularity of Kotlin: Kotlin gained significant traction, especially after becoming the preferred language for Android app development, and its popularity continued to rise;
7. 2021-2022 - Kotlin Becomes More Popular Than Java for Android Development: Kotlin surpassed Java in popularity for Android app development, driven by its modern features and official endorsement by Google.

But it's important for us to understand the key differences between these two languages. How do they compare syntax and other features, considering that Kotlin has surpassed Java in popularity while Java still holds its ground?

Kotlin and Java are similar in their core principles but differ significantly in many aspects. One language might be simpler, with a vast community that makes problem-solving much quicker. The other is more modern, packed with features that simplify coding and adding new functionality. Let's take a look at a comparison table highlighting the key aspects of these two programming languages:

The table provides a comparison, but let’s dive deeper into some of the points. For instance, let's talk about syntax and compare how identical functions look in Java and Kotlin, such as a sum function:

Above, you can see the syntax for the simplest main method and a sum method that takes two numbers and returns their sum.

As you can see, Java's syntax is quite verbose, partly because it's an object-oriented language and because it requires specifying all details when writing methods (functions). However, this also makes Java's syntax more explicit, as every detail is outlined in the code, making it easier for other developers to understand what's written.

Now, let's take a look at Kotlin's syntax:

As you can see, Kotlin's syntax is visually simpler, which is partly because Kotlin also supports functional programming. This leads to a slightly different coding style. For example, we don't need to specify a Main class to run the program, and the main function itself is much simpler. We just declare the main function and write the logic we need.

This syntax is easier to write but can be more challenging to read. In Java, every detail is explicitly stated in the code, whereas Kotlin's syntax is more streamlined. Ultimately, which approach is better depends on your preference.

Kotlin also supports object-oriented programming for writing code.

Let's quickly compare the syntax in the context of OOP for both languages so everyone can decide which is more convenient for them. We'll start with the Java syntax, where we create a Person class and call the "introduce" method from that class:

As you can see, the situation is similar to the basic syntax — this code is lengthy and overloaded. While some libraries can help reduce the amount of code, we are focusing on pure Java syntax. We must explicitly write getters and setters to access private fields, which we need for encapsulation. We also need to explicitly define the class constructor to create a method and call it on an instance of the Person class.

Now, let's take a look at the syntax for creating a similar class in Kotlin:

Here, Kotlin clearly wins in terms of code brevity and functionality. The constructor in Kotlin is built into the class declaration and is called the primary constructor, which is invoked when creating an object of the class. We also don't need to write getters and setters manually, as they are built into Kotlin's functionality. However, we can still customize them if needed.

It seems that Kotlin excels in the simplicity and functionality of syntax for writing and using classes, although Java remains more explicit due to its detailed specifications.

Performance in Java and Kotlin is very similar, as both languages compile code into bytecode using the JVM. This is why the languages are so alike and often used together. Kotlin allows using Java libraries and code without needing to rewrite them. So, we can use Kotlin classes and code within Java, but that's not the focus here.

Let's take a look at the comparison table of Kotlin and Java performance across different scenarios and aspects:

Determining a winner here is quite challenging, as both programming languages handle optimization very well. So, we'll leave the final decision open and let users decide what suits them best. However, let's examine another crucial aspect of optimization — Memory Management. Here, we might identify a winner, even if the difference is very slight:

Memory Management

When it comes to memory management, Java and Kotlin handle things a bit differently, but both ultimately rely on garbage collection to manage memory.

Java employs an automatic garbage collector that reclaims memory by identifying and removing objects that are no longer in use. However, Java developers must manage memory indirectly by avoiding leaks and optimizing memory usage. Java's garbage collection can introduce performance overhead, particularly with larger applications or in environments where low latency is crucial. This system allows Java to handle memory management effectively, but it requires careful attention to avoid pitfalls like excessive garbage collection pauses.

Kotlin, being fully interoperable with Java, leverages the same JVM garbage collection mechanisms. Kotlin introduces several features to improve memory management and reduce leaks. Its support for properties and data classes can lead to cleaner code and fewer manual memory management tasks. Additionally, Kotlin's null safety and smart casts help prevent common programming errors that could lead to inefficient memory use. Although Kotlin benefits from the JVM's established garbage collection, it simplifies memory management through its modern language features, making code less prone to memory-related issues.

Thus, in terms of memory management, Kotlin has a slight edge over Java, although the two languages still closely compete.

Interoperability between Java and Kotlin is a key feature of Kotlin, making it easier for developers to transition from Java or use Java libraries within Kotlin applications.

Java and Kotlin Interoperability

Kotlin is designed to be fully interoperable with Java, meaning you can call Java code from Kotlin and vice versa without needing extensive modifications. This interoperability ensures that developers can gradually adopt Kotlin in existing Java codebases or mix the two languages within a single project, leveraging the strengths of both.

Using Java Libraries in Kotlin

It is straightforward, thanks to Kotlin's excellent Java interoperability. You can use Java libraries directly in Kotlin code as native Kotlin libraries. Kotlin handles Java's verbose syntax and offers concise alternatives, but Java classes and methods can be used without modification. For instance, Java libraries can be called, instantiated, and manipulated like Kotlin classes, making it easy to leverage existing Java ecosystems.

Using Kotlin Libraries in Java

It is also possible, though it requires some considerations. While Kotlin libraries can be used in Java code, certain Kotlin-specific features, such as extension functions or data classes, might not be fully accessible or require additional effort. Kotlin generates Java bytecode, which Java can consume, but certain Kotlin constructs might not map directly to Java, necessitating some adaptation when integrating Kotlin libraries into Java projects.

Overall, Kotlin's interoperability with Java facilitates smooth integration and incremental adoption, enabling developers to leverage the strengths of both languages within their projects.

Note

It's also worth noting that transitioning from Java to Kotlin will be relatively easy for you, but moving from Kotlin to Java might be a more challenging task and decision.

Let's talk about the tools we can use to develop applications and products in these two programming languages. We'll look at the supported IDEs and build tools.

IDE Support for Java:

Java enjoys robust support across various IDEs, including:

• IntelliJ IDEA: Developed by JetBrains, it's the most popular IDE for Java with powerful features for coding, debugging, and integration with build tools;
• Eclipse: A widely used, open-source IDE known for its extensibility and support for Java development through plugins;
• NetBeans: Another popular choice, especially in academic settings, providing an integrated development environment with good support for Java.

IDE Support for Kotlin:

Kotlin is fully supported by several modern IDEs:

• IntelliJ IDEA: The primary IDE for Kotlin, offering excellent integration and comprehensive support, including advanced code analysis and refactoring tools;
• Android Studio: Built on IntelliJ IDEA, it provides strong Kotlin support for Android development, including Kotlin-specific features and tools;
• Eclipse: Kotlin support in Eclipse is available through plugins, but it's less seamless compared to IntelliJ IDEA.

Build Tools and Dependency Management:

Both Java and Kotlin use similar build tools and dependency management systems:

• Maven: A widely-used build tool for Java projects, supporting dependency management and project configuration through XML files;
• Gradle: A versatile build tool favored by both Java and Kotlin developers, offering flexible build configurations and dependency management with Groovy or Kotlin DSL;
• Kotlin DSL: Gradle supports Kotlin DSL for build scripts, providing a more idiomatic way to define build configurations in Kotlin.

These tools and IDEs contribute significantly to the efficiency and productivity of Java and Kotlin developers, offering a range of features to streamline development, debugging, and deployment processes.

As I mentioned earlier, Java has a stable and massive community, while Kotlin's community is still growing and developing. Because of this, finding an answer to a question on Stack Overflow might take longer for Kotlin. But let’s not speculate — let's look at the charts to see the difference in activity between Java and Kotlin on Stack Overflow.

The chart was taken from official Stack Overflow statistics using the Stack Overflow Trends service:

We can see that Java has a significantly larger community compared to Kotlin, but we can also observe that the Java community is shrinking while Kotlin's is rapidly growing.

Let's also take a look at the statistics gathered by RedMonk. These guys collect data on all programming languages, based on Stack Overflow Trends as well as the GitHub archive, to get a comprehensive view of the popularity and usability of a programming language:

If we look at this graph, we can see that Java is a top language, ranking third in popularity. Meanwhile, Kotlin is hard to spot on the graph, as it ranks 17th among all programming languages. It's worth noting that this data is from 2024.

However, don't conclude that "Kotlin isn't popular" just because it's searched less. Kotlin is a fresh and modern programming language that is gaining incredible popularity.

Here's what RedMonk has to say about Kotlin and its rapidly growing popularity:

This further confirms Kotlin's rapid rise in popularity. But let's also look at another important statistic—the job market for both programming languages.

Job Market and Demand for Java vs. Kotlin Developers

1. Java:
   • Popularity: Java remains one of the most popular programming languages. It's widely used in the corporate sector for developing backend applications, web services, and Android development;
   • Job Opportunities: Due to its maturity and widespread use, Java offers more job opportunities, especially in large companies and financial institutions;
   • Where to Look: Java is in demand across various fields, including fintech, big data, and enterprise applications.
2. Kotlin:
   • Popularity: Kotlin is rapidly gaining popularity, especially in Android mobile development, since Google has made it the official language for the platform;
   • Job Opportunities: Although there are fewer job openings compared to Java, the number is growing, particularly in companies focused on mobile app development;
   • Where to Look: Kotlin is sought after in startups and companies focused on mobile development.

Where is it Easier to Find a Job?

• Java: It is easier to find a job due to the larger number of openings and the diversity of applications. If you're aiming for a stable job in a large company, Java would be the better choice;
• Kotlin: While the job market is smaller, demand for Kotlin is growing, especially among Android developers. If you're focused on mobile apps and startups, Kotlin may be more promising.

Conclusion: Java is a stable language, but it's losing popularity in the job market as it falls behind many modern languages regarding features and coding convenience.

After a thorough comparison of the syntax and popularity of both languages, it's time to discuss where each programming language is best utilized.

Where to Use Java

We've established that Java is often used for the development and maintenance of a vast number of applications, both web and desktop. Let's take a closer look at where Java excels:

• Enterprise Applications: Java is ideal for large-scale enterprise applications due to its stability and scalability, which are essential for maintaining critical business operations;
• Web Applications: Use Java for building robust and secure web applications. Its mature frameworks, like Spring, provide comprehensive support for developing and maintaining large-scale web services;
• Big Data Technologies: Java is a go-to language for big data projects, with frameworks like Apache Hadoop and Apache Spark built on Java, making it essential for processing large datasets;
• Cross-platform Applications: Java's ability to run on any platform that supports the JVM (Java Virtual Machine) makes it suitable for applications that need to be deployed across multiple operating systems.

Where to Use Kotlin

Given that Kotlin is currently the best programming language for Android applications, let's explore where Kotlin truly shines:

• Android Development: Kotlin is the preferred language for Android app development. It's more concise than Java, reduces boilerplate code, and is officially supported by Google, making it the best choice for modern Android projects;
• Interoperability with Java: Kotlin is fully interoperable with Java, which means you can use it in projects that already have a Java codebase, allowing for gradual migration and integration of modern language features;
• Server-side Development: Kotlin is increasingly used for server-side applications, especially in scenarios where a modern, expressive, and concise language is preferred. It integrates well with frameworks like Ktor and Spring;
• Multiplatform Projects: Kotlin's multiplatform capabilities allow you to use a single codebase across different platforms like Android, iOS, and web, which is ideal for projects requiring cross-platform compatibility.

These use cases highlight the strengths of each language based on extensive research and usage patterns.

Let’s now talk about successful Java and Kotlin projects that have gained worldwide recognition and are still in use today, maintained in their respective programming languages:

Java Projects:

• LinkedIn: Originally built with Java, LinkedIn uses it for scalability and handling millions of users globally;
• Amazon Web Services (AWS): Java powers many of AWS's services, showcasing its strength in building reliable and scalable cloud infrastructure;
• Netflix: Uses Java for backend microservices that need to scale globally, handling millions of concurrent users.

Kotlin Projects:

• Pinterest: Migrated to Kotlin for Android development to reduce boilerplate code and improve productivity;
• Trello: Uses Kotlin in its Android app to take advantage of its expressive syntax and improved error handling;
• Square: Square, known for its payment solutions, adopted Kotlin for its Android development to enhance code readability and maintainability, leading to a more efficient development process.

As you can see, Java is behind many older, well-established applications and products, while Kotlin is being used for more modern and promising projects, particularly in Android development.

Conclusion

Let's summarize the article by determining exactly how and when to use each programming language when choosing between Kotlin and Java.

Summary of Key Points

Java and Kotlin each have distinct strengths that cater to different needs in software development. Java excels in large-scale enterprise applications, web services, and big data technologies due to its robustness, extensive ecosystem, and cross-platform capabilities. It's the go-to language for traditional enterprise environments and high-performance backend systems. Kotlin, on the other hand, has gained prominence for Android development because of its modern syntax, reduced boilerplate code, and seamless interoperability with Java. Its use is expanding into server-side development and multiplatform projects, making it a versatile choice for modern applications.

Future Trends in Java and Kotlin Development

The future of Java will likely focus on enhancing its performance and features to stay relevant in evolving tech landscapes. Java continues to receive updates that improve its usability, including new language features and performance optimizations. Kotlin's future looks promising as it continues to grow in the Android ecosystem and beyond. Its multiplatform capabilities suggest a trend towards more unified codebases that span across mobile, web, and server applications. As the demand for cross-platform solutions increases, Kotlin's role in simplifying and streamlining development across different platforms is expected to grow.

Final Recommendations for Developers

For developers deciding between Java and Kotlin, the choice largely depends on the project requirements and long-term goals. If working on large-scale enterprise systems, legacy projects, or backend services where stability and extensive libraries are crucial, Java remains a strong choice. For modern Android app development, Kotlin is highly recommended due to its concise syntax, modern features, and official support from Google. For projects requiring cross-platform compatibility or integrating with existing Java codebases, Kotlin offers significant advantages. Overall, both languages have their place, and understanding their strengths will help developers choose the right tool for their specific needs.

What are the advantages of using Kotlin over Java?

Kotlin offers a more concise syntax, reduces boilerplate code, and includes modern features like null safety and extension functions, which enhance developer productivity and code safety.

Can I use Kotlin for Android development?

Yes, Kotlin is officially supported by Google for Android development and is often preferred for its modern features and improved developer experience.

Is Java still relevant in today's development landscape?

Yes, Java remains highly relevant for enterprise applications, web services, and big data technologies due to its stability, extensive libraries, and cross-platform capabilities.

How do I migrate a Java project to Kotlin?

You can gradually migrate a Java project to Kotlin by adding Kotlin files to your project and using Kotlin's interoperability with Java. Many IDEs offer tools to assist with the migration process.

What are the learning curves for Java and Kotlin?

Java has a steeper learning curve for beginners due to its verbose syntax and complex features. Kotlin is generally considered easier to learn due to its more concise syntax and modern features, especially for those already familiar with Java.