Kotlin vs. Java – What Are the Key Differences?

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Krzysztof Jackowski

Updated Oct 17, 2023 • 21 min read
Kotlin & Java Comparison

In the world of programming, Kotlin and Java have established themselves as influential languages. As you navigate your path in software development, understanding these languages and their differences is vital.

This comparison dives into the nuances of both Kotlin and Java, with an emphasis on their functionality, syntax, and the robust code they produce. With this knowledge, you can make an informed decision on which language best serves your project needs.

Java and Kotlin have their unique strengths and weaknesses. Java has been praised for its wide use, mature ecosystem, and implicit widening conversions. It, however, has been criticized for its boilerplate code and the potential for null pointer exceptions, which could introduce errors in the code. On the other hand, Kotlin is lauded for its efficiency, especially in developing android applications. It provides a more streamlined syntax, reducing the amount of code written, and has features such as the ternary operator, which is lacking in Java.

Introduction to Kotlin and Java

Kotlin and Java are both powerful programming languages with varied features that make them suitable for different projects. Java, a stalwart in the software development industry, and Kotlin, a more recent entrant, have different approaches to some programming concepts. For instance, both languages support Lambda expressions, but Kotlin takes it a notch higher with inline functions and operator overloading for more performant custom control structures. Kotlin also introduces Smart Casts, a feature not present in Java, that simplifies the handling of variables.

Brief Overview of Kotlin

Kotlin, a statically typed programming language, runs on the Java Virtual Machine (JVM). It is designed to interoperate fully with Java and other JVM languages. Kotlin stands apart with its modern features such as Lambda expressions, inline functions, and operator overloading, which enhance the language's expressiveness and code readability. Furthermore, Kotlin's Smart Casts feature significantly reduces the need for explicit type conversion in the code, making it more readable and concise.

Brief Overview of Java

Java, an object-oriented programming language, has been a cornerstone in the software development industry for over two decades. It is renowned for its platform independence, allowing developers to "write once, run anywhere". Java supports Lambda expressions, which provide functional programming capabilities and can simplify code. However, unlike Kotlin, it does not support inline functions, a feature that could potentially optimize performance by reducing function call overhead.

Historical Background of Kotlin and Java

Understanding the historical background of Kotlin and Java provides valuable context to their evolution and design decisions. Java, developed by Sun Microsystems in the mid-1990s, has undergone numerous updates to keep pace with modern programming needs. Kotlin, on the other hand, is a relatively new language developed by JetBrains. It was designed to address certain shortcomings in Java, such as verbosity and null safety issues. Both languages have embraced lambda expressions, indicating a shift towards functional programming paradigms in recent years.

Origin and Evolution of Java

Java, a widely used programming language, was developed by James Gosling and his team at Sun Microsystems in 1995. Its main aim was to design a platform-independent language for software development. As an object-oriented language, it revolutionized the world of web applications with its "Write Once, Run Anywhere" policy. Over the years, Java has evolved significantly with numerous version updates, each one improving upon its performance, security, and coding efficiency.

Origin and Evolution of Kotlin

On the other hand, Kotlin is a more recent arrival in the programming world. It was introduced by JetBrains in 2011 with the intention of addressing some of the issues developers faced with Java, particularly in terms of verbosity and null safety. Kotlin was officially endorsed by Google for Android app development in 2017. Since then, its popularity has surged, thanks to its concise syntax and interoperability with Java.

Understanding the Kotlin vs Java Debate

The Kotlin vs Java debate is fueled by the strengths and weaknesses of both languages. While Java has a long history and wide acceptance, Kotlin brings in contemporary features and improvements over Java. Understanding the nuances of both languages can help you make an informed decision on which one to use for your programming needs.

Why Compare Kotlin vs Java?

The comparison between Kotlin and Java is natural since both languages are used for similar purposes, particularly in Android app development. Java has been the traditional choice for developers, but Kotlin's rise in popularity since its endorsement by Google has sparked interest. It is essential to compare Kotlin and Java to understand their advantages and disadvantages, and to determine which language better suits your specific project requirements.

Common Use Cases for Kotlin and Java

Both Kotlin and Java have their own strengths that make them suitable for different use cases. Java has been extensively used for building enterprise-grade server-side applications due to its robustness and scalability. It also finds use in Android app development, web application development, and big data technologies. Kotlin, while being a powerful tool for Android app development, is also gaining traction in server-side applications due to its concise syntax and advanced features. The use of Java vs Kotlin largely depends on the specific needs of the project and the preferences of the development team.

Key Differences Between Kotlin and Java

When it comes to the comparison between Java and Kotlin, there are several key differences to consider. These differences primarily revolve around the concepts of object-oriented and functional programming, null safety, extension functions, and exception handling. Java is an object-oriented programming language with a rich history and a wide range of applications. On the other hand, Kotlin combines the features of both object-oriented and functional programming, giving it a unique edge over Java. Interestingly, while Java supports implicit conversions, Kotlin does not offer this feature. These differences have significant implications on the type of code written by Java developers and those using Kotlin.

Null Safety in Kotlin vs Java

One of the most notable differences between Kotlin and Java is how they handle null safety. In Java, null variables or objects are part of the Java language, which can often lead to NullPointerExceptions. This can cause significant issues as developers have to constantly check for and handle these exceptions. In contrast, Kotlin offers a feature known as non-nullability. This means that you cannot assign a null value to a variable unless it is explicitly declared as nullable. This feature, combined with Kotlin's comprehensive exception handling, greatly reduces the risk of NullPointerExceptions, making Kotlin a safer choice for developers.

Extension Functions: Kotlin's Advantage

Kotlin offers a significant advantage over Java in the form of extension functions. Unlike Java, Kotlin allows developers to extend the functionality of classes without having to inherit from them. This means that developers can add new functions to an existing class without modifying its source code. This feature significantly enhances the flexibility of Kotlin, allowing developers to write code that is more concise, readable, and maintainable. This is one of the key reasons why many developers prefer Kotlin over Java.

Checked Exceptions in Java and Kotlin

Another area where Kotlin and Java differ significantly is in their handling of checked exceptions. In Java, checked exceptions are those that must be either caught or declared in the method where they occur. This can lead to verbose and cluttered code. However, in Kotlin, there are no checked exceptions. This can simplify the code and make it more readable, although it does mean that developers need to be more careful to avoid unexpected exceptions.

Handling Exceptions in Java

Exception handling in Java is achieved through the use of try-catch blocks. When an exception occurs, the Java runtime system will attempt to find an appropriate exception handler, which is a block of code designed to handle that particular type of exception. If it finds a matching handler, it passes the exception to the handler to resolve. However, if it doesn't find a matching handler, it passes the exception up the calling hierarchy until it finds one or until it reaches the top level of the program. This can lead to verbose and sometimes confusing code, particularly in larger applications.

Handling Exceptions in Kotlin

When it comes to handling exceptions, Kotlin introduces a more streamlined approach compared to Java. Instead of the traditional try-catch blocks, Kotlin encourages the use of higher-order functions and extension functions to handle exceptions. This results in cleaner, more readable code and reduces the chances of unhandled exceptions.

Functional Programming: Kotlin vs Java

In the debate between Kotlin and Java, one of the key talking points is the support for functional programming concepts. While both Kotlin and Java support OOPs and functional programming, Kotlin provides a more comprehensive and expressive functional programming model. This feature, along with its interoperability with Java, makes Kotlin a flexible choice for modern programming needs.

Data Classes: A Kotlin Feature

Data classes are a unique feature in Kotlin, similar to records introduced in Java 8. They are designed to hold data, and automatically generate essential methods like toString(), equals(), and hashCode(). This eliminates the need for boilerplate code, making your codebase more concise and easy to manage.

Smart Casts in Kotlin: An Improvement over Java

Kotlin improves upon Java's type casting with the introduction of smart casts. In Java, explicit type casting is often required, which can lead to redundant casts and potential ClassCastException. Kotlin's smart cast feature intelligently handles these scenarios, automatically casting objects within a context where it's safe to do so.

Delving Deeper: Unique Features of Kotlin and Java

When we delve deeper into the unique features of Kotlin and Java, we find that each language has its own strengths. The Java compiler is robust and time-tested, creating optimized bytecode that runs efficiently on the Java Virtual Machine. Java compiles your code into machine language, ensuring high performance. On the other hand, the Kotlin compiler is designed for safety and interoperability. It checks for common programming mistakes at compile-time and can compile your code into either Java bytecode or JavaScript, providing flexibility for cross-platform development.

Coroutines Support in Kotlin

When it comes to handling long-running operations, Java offers the ability to create multiple threads in the background. However, managing multiple threads can be a complex task for developers. Kotlin developers, on the other hand, have a more streamlined solution at their disposal. Kotlin provides support for coroutines. These can suspend the execution of blocking threads at particular points, significantly simplifying the task of managing concurrent operations.

Public Fields and Implicit Conversions in Java

Java provides a feature known as public fields or non-private fields. This can be quite useful in cases where the callers of an object need to modify the object's representation. The convenience arises from the fact that the developer can change the object's representation without having to adjust the callers. This feature allows fields to be public, thus ensuring that the public API remains unchanged and the program maintains a high level of maintainability. This is in contrast to Kotlin, which does not support public fields.

Comparing Kotlin and Java in Practical Scenarios

Java is a widely used general-purpose language, popular worldwide for its versatility. Kotlin is a younger competitor, not as prevalent as Java, but has shown significant growth, particularly in the field of Android development. In fact, Google recognized Kotlin as their second official language for Android development in 2017. Two years later, Kotlin was declared as the preferred language for Android development, leading to a surge in its popularity and usage.

Android App Development: Kotlin vs Java

The Java vs Kotlin debate is quite relevant when it comes to Android app development. Both languages have their unique benefits and drawbacks. For instance, the Kotlin language has built-in null safety, which helps avoid NullPointerException errors. It also supports data classes and lambdas, helping developers code more concisely and expressively. However, Kotlin does not enjoy as much support from the Android community as Java. As a newer language, there are still aspects of Kotlin that need refinement. Therefore, whether Kotlin or Java is the better choice depends largely on the specific requirements of your project. If you're starting a new project from scratch, Kotlin may be the more concise language to use.

Backend Development: Java vs Kotlin

When it comes to backend development, the Java vs Kotlin debate remains relevant. Both languages have their strengths and weaknesses. Kotlin offers many features that are not available in Java, such as built-in null safety and support for data classes and lambdas, which can make your code more concise and expressive. However, Kotlin does not have the same level of support from the Android community as Java, and being a relatively new language, there are aspects that need to be refined. Therefore, the choice between Kotlin and Java will depend on the specific needs of your project.

Kotlin vs Java: Performance and Memory Usage

When selecting a language for your project, considering performance and memory usage is crucial. Kotlin and Java, both JVM languages, are quite similar in these aspects. This is due to their similar compilation processes and runtime environments, originally designed to target embedded systems with limited resources. The JVM's multiplatform approach encourages runtime optimizations, which has influenced performance and memory usage in both languages.

However, there are minor performance differences between Kotlin and Java, mostly due to their distinct features. For instance, Kotlin's inline functions, which are a type of higher-order functions, avoid a function call thereby improving performance. On the contrary, Java invokes additional overhead memory. This is because Kotlin's inline functions allow the function code to be expanded in place, which sometimes results in more efficient bytecode. Java, however, lacks this feature.

It's important to note that the JVM was primarily created with a focus on performance efficiency. This focus is evident in both Java and Kotlin, especially considering their use in the development of software for embedded systems. This is because embedded systems typically have limited resources and thus require languages that are efficient in terms of memory usage and performance.

Overall, while Kotlin and Java have similar performance and memory usage, some of Kotlin's unique features, such as inline and higher-order functions, can provide slight performance improvements. However, these differences are minor and likely won't significantly impact the performance of your application. Instead, the choice between Kotlin and Java should be based on other factors such as the specific requirements of your project and your familiarity with each language.

Making the Leap: Transitioning from Java to Kotlin

Transitioning from Java to Kotlin can be a smooth process due to their many similarities. However, understanding the differences between these two languages is key to a successful transition. Kotlin offers several features that can enhance your coding experience, like null safety, smart casts, and extension functions. It's important to familiarize yourself with these features to fully leverage the benefits of Kotlin.

Similarities Between Kotlin and Java

Despite their differences, Kotlin and Java share several commonalities. For instance, their approach to data transfer objects is quite similar. Both languages have constructs that hold information about data or state and include methods like toString, equals, and hashCode. In Java, these are known as records, while in Kotlin they're called data classes. Furthermore, both languages support lambda expressions, a feature that allows you to create anonymous functions. Understanding these similarities can make transitioning from Java to Kotlin easier.

Differences to Keep in Mind While Transitioning

While there are many similarities between Kotlin and Java, there are also key differences to note. For example, Kotlin's syntax is more concise, which can make your code easier to read and write. Additionally, Kotlin has built-in null safety to prevent null pointer exceptions, a common source of bugs in Java. Kotlin also supports coroutines, which allow for simpler asynchronous programming. Being aware of these differences can help you avoid common pitfalls when transitioning from Java to Kotlin.

Kotlin vs Java: Which is Better for Your Project?

The choice between Kotlin and Java depends largely on the specific needs of your project. Kotlin, being a more modern language, has a concise syntax and requires less code. It's officially supported by Google for Android development and offers unique features like coroutines and null safety. On the other hand, Java has been around for longer and has a robust community, extensive documentation, and a vast ecosystem of libraries and tools. It's a general-purpose programming language that supports almost any operating system, making it a versatile choice for multiplatform projects. Choosing whether to use Kotlin or Java for your project should be based on these factors, as well as your personal preference and familiarity with each language.

Advantages and Disadvantages of Kotlin

Kotlin offers several advantages as a modern programming language, but it also presents a few challenges. On the plus side, Kotlin is a highly declarative language, allowing developers to code in a clear and concise manner. However, its compilation speed may be slower compared to some other languages due to the amount of boilerplate it generates for the JVM. Furthermore, as Kotlin is not as popular as some other languages, the developer community is relatively small. This means that there are fewer learning resources and professional aids available for those starting with Kotlin.

Advantages and Disadvantages of Java

Java, on the other hand, has a long history and a large pool of skilled developers, making it a robust and reliable choice for many projects. It's platform independent, which means the written code can be run on various devices without modification. Java also provides checked exceptions, a feature that enhances error detection and resolution. However, while Java's extensive documentation and large array of third-party libraries are beneficial, it can also make the language more complex and challenging for beginners to learn and navigate.

Concluding Thoughts on Kotlin vs Java

Both Kotlin and Java are powerful general-purpose languages popular for developing a variety of applications, including Android apps. Each has its unique features, and choosing between the two often depends on the specific needs of the project. Transitioning between the two languages requires a clear understanding of their features and differences.

Final Verdict: Choosing Between Kotlin and Java

The choice between Kotlin and Java boils down to your project requirements, experience level, and personal preference. While the learning curve for Kotlin might be steeper due to its smaller community, it offers several modern features and a more streamlined syntax. Java, on the other hand, is a tried-and-true language with a vast library and a large developer community. When transitioning between the two, it's crucial to understand how common concepts like data transfer objects and lambda expressions operate differently in each language.

Looking ahead, both Kotlin and Java show promising trends. Kotlin's modern features like null safety, smart casts, and coroutines signal a growing preference for more streamlined and efficient coding. Java, on the other hand, continues to be a reliable choice for large-scale, complex projects due to its robustness and extensive libraries. As technology evolves, both languages are likely to adapt and introduce new features to meet the needs of developers and the wider tech industry.

Over the past few years, Kotlin has shown a promising upward trend in its usage. This can be attributed to its modern features, robustness, and compatibility with Java. Kotlin's adoption rates have significantly increased, especially in Android app development, mainly because of its concise syntax and interoperability with Java. This growth trend shows a promising future for Kotlin, with more developers likely to transition to it for its practical advantages.

In contrast, Java, being a veteran language, has maintained a steady user base. Although it's perceived as less modern compared to newer languages like Kotlin, Java's mature ecosystem and broad range of applications keep it relevant. Its usage in enterprise systems and backend development remains robust. However, the trend shows a slow but steady decline in Java's popularity, especially in areas where Kotlin and other modern languages have started to gain ground.

Whether you're a seasoned developer or a beginner keen on exploring Kotlin and Java, there are numerous resources available to help. Books, online tutorials, coding bootcamps, and documentation serve as educational tools, while communities and forums offer a space for interaction, queries, and discussions. These resources can significantly aid your learning journey and decision-making process in choosing between Kotlin and Java.

Educational Resources for Java and Kotlin

Both Kotlin and Java have a wealth of educational resources available. For Kotlin, you can explore topics such as lambda expressions, null-safety, smart casts, and coroutines through online tutorials and documentation. Java, on the other hand, offers extensive resources on topics like implicit conversions, public fields, and handling exceptions. These resources are designed to cater to learners of different levels, from beginners to experts. Taking advantage of these resources can help you gain a deeper understanding of both languages.

Communities and Forums for Kotlin and Java Developers

Participating in communities and forums can be a valuable part of learning and applying Kotlin and Java. These platforms offer a space for developers to share experiences, ask questions, and discuss issues. You can find practical insights, code snippets, and solutions to common problems. Some of the popular communities include Stack Overflow, Reddit, and the official Kotlin and Java forums. Engaging in these communities can not only enhance your knowledge but also connect you with other developers in the field.

Making the Right Choice in the Kotlin vs Java Debate

Deciding between Kotlin and Java for your development projects, particularly mobile apps, can be a complex task. Both languages have their strengths and weaknesses. Java, an open-source language, has stood the test of time and has a large community of developers. On the other hand, Kotlin, an improved version of Java, is gaining popularity due to its compatibility with existing Java code and its ability to generate native code for multiple platforms.

When dealing with mobile development, one of the key considerations is the handling of lengthy operations and the creation of multiple background threads. Kotlin excels in this area with its support for coroutines, which simplifies the process. Another advantage of Kotlin is its type inference and smart casts feature, which reduces the need for explicit casting checks in your code. You can even use Java code from Kotlin, making the transition smoother.

However, the choice between Kotlin and Java does not necessarily have to be binary. Both languages can be used in conjunction, capitalizing on their strengths. The choice ultimately depends on your project requirements, your familiarity with the languages, and your willingness to learn new concepts. So, dive into the world of Kotlin and Java, explore their unique features, and make an informed decision that best suits your needs.

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