Irrspective of a number of software, app, website, and other development languages available in the tech world, Kotlin and Java are most preferred by many software and mobile app development companies. They are the two most powerful languages that are used in object-oriented programming. But both are used for different purposes and they are 100% interoperable.

As an older language, Java has been around in the industry for years and is mainly used for enterprise application development. Whereas, Kotlin came into context recently and has become popular to be use as the finest Android application development language.

However, the biggest question come into the minds of the developers today that which is better – Kotlin or Java. Although, both the languages are suitable for Android development, still they comprise some pros and cons that makes them different to each other. 

Java possesses a vast community of users and developers and a plethora of libraries, whereas Kotlin offers contemporary features and concise syntax that appeals the developers for their development requirements. Both the languages are used for building applications for Java Virtual Machine (JVM), but they are different in terms of features, syntax, and performance. 

This article comprises a refined detail and discussion about this concept to understand which language holds supremacy over the other. 

About Kotlin

Kotlin 1.0 debuted in 2016 and is officially introduced by Google in 2019 as a recommended language by the company for building Android apps. It offers trimmed coding and fast compilation of application programs. This programming language utilizes JVM that combines the features of OOPs with functional oriented programming. It supports a variety of extension functions without even changing the code in anyway. In fact, the code in Kotlin can be written using IDE or the command-line interface. The smart feature casting in Kotlin helps the users to cut down the costs of application and improve its performance and speed.

Benefits of Kotlin

  • The usage of Kotlin’s multiplatform framework enables the developers to extract a common codebase that will target all the codebases at the same time.
  • The language offers built-in null-safety support full on old Java-style APIs that is a lifesaver, especially on Android.
  • Kotlin is more expressive and concise than Java that leaves no room for error.
  • Here large apps are divided into smaller ones facilitating understandable coding norms and user-friendly nature.
  • Kotlin is statically-typed programming language that can be easily read and write and allows the exchange and usage of information from Java in numerous ways.
  • It offers a simple and most automated way of creating data classes and uses a lot of function types and specialized language structures like lambda expressions.
  • Kotlin helps the developers to create extension functions and deploy code and maintain it at scale.

About Java

As a multi-platform, network centric, and object-oriented programming language, Java was first released by Sun Microsystem in 1995 and was later acquired by Oracle Corporation. Java facilitates writing code once and then running it on almost any computing platform. The language facilitates distributed computing as network-centric and allows automatic memory management due to its multithreaded feature.

Benefits of Java

  • Java facilitates excellent performance, and the multi-threaded environment allows the developers to perform a number of tasks simultaneously in the program. 
  • A large pool of skilled developers develops Java-based programs and check exceptions that improve error detecting and solving. 
  • Java comprises a huge array of easy-to-navigate third-party libraries, and allows the users to form standard programs and reusable code. 
  • The detailed documentation of the app programs can be easily created using Java.

Performance: Kotlin vs. Java

When comparing performance of Kotlin and Java, it is important to understand that both the languages run on (JVM). Hence, they generally comprise minimal runtime performance differences. However, there are some aspects where Kotlin offers some advantages to the users and major differences here are more related to code design and language features than inherent performance characteristics.

#1 Startup time – Kotlin takes a bit longer start-up time because of the additional bytecode and runtime libraries required for the features like extension functions and null safety. However, the difference is generally negligible in majority of applications.

#2 Runtime Performance – Kotlin and Java both perform work equally at runtime as they share the same JVM. The choice of language slightly impacts the speed of execution.

#3 Consumption of Memory – The smart casting and null safety feature of Kotlin results in highly efficient memory usage with fewer null pointer exceptions. This ultimately leads to lower memory consumption in comparison to Java development.

#4 Method Overhead – The support of Kotlin for extension functions and other language features give room to a small method called overhead. This overhead is however negligible unless the developers are working in the performance-critical sections.

#5 Compile – Time Performance - The compilation time of Kotlin can be longer than Java for large projects and this is primarily due to the additional language features. However, no significant difference is seen generally while practicing.

#6 Coroutines – The native support of Kotlin for coroutines leads to more efficient asynchronous code in comparison to the traditional thread-based concurrency of Java. However, the performance benefits are mostly based on the use case.

Why to Compare Kotlin Vs. Java?

As discussed earlier, Java is a generally-used language for developing simple Android apps, but when it is combined with Python and JavaScript, it becomes the most popular and powerful language in the world.

One year after Kotlin’s launch, Google recognized it as their second official language for Android app development and in 2019, it was regarded as the most favored programming language for creating Android apps at Google due to its incredible growth. Hence, comparing both the popular platforms and languages makes sense.

Key Differences Between Kotlin and Java

Now, when we got a bit of the context. Let’s dig out how the popularity of Java and Kotlin is impacting each other and whether both of them would replace each other. However, there are a lot misconception on this topic, looking close at their differences can conclude this discussion.

#1 Null Safety – The Java-based famous NullPointer Exceptions provide null value to any variable. For example, suppose users attempt use an object reference that possesses a null value. In such a case, the NullPointer Exceptions of Java come into context and gives room to an exception that developers need to handle.

In contrary, attributing null values to variables or by default objects is not possible in Kotlin. If it is attempted, the code failure during the compilation time is quite possible. Hence, no NullPointer Exceptions are there in Kotlin. On the other hand, if the developers wish to assign a null value, marking out the variable in question as nullable is explicitly possible. One should add a question mark to do so:

#2 Code – The most significant difference between Kotlin and Java is that Kotlin requires less coding than Java. Kotlin is regarded as a very concise language that reduces the chance of occurrence of errors and simplifies the work of the developers.

Kotlin is quite helpful in writing and managing large projects and requires fewer lines of programming compared to Java for writing the exact similar functions. Also, the Kotlin developers know best about keeping codes short and straightforward without even compromising the readability of the syntax.

#3 Extension Functions – Kotlin developers can extend the functionality of classes without necessarily inheriting from a class that never happens with Java. For performing the extension function in Kotlin, the developers should prefix the class to the name of the extension function created by using the ‘.’ Notation. Whereas in Java, a developer should create a new class with inheriting the functions from the parent class to extend the functionality of an existing class. In simple words, the extension function is not available in Java development.

#4 Data Classes – Java developers need to establish the variables or fields to store the data, the getter/setter, and the constructor functions for the fields/variables and other functions such as the hashCode()equals() and toString(). The truth is, such classes are meant to mainly store data and have a little to zero functionality.

On the other hand, Kotlin developers are allowed to create classes to hold data in a more straightforward way by simply including the ‘data’ keyword in the class definition. Then, the constructor, the getter, and the setter functions will automatically be generated by the compiler for several fields/variables.

#5 Smart Casts – For casting an object in Java, the developers should check the variables’ type while operation. However, the casting checks in Kotlin are smartly handled by the smart casts feature. The redundant casts with stable values get automatically managed by the Kotlin’s intelligent compiler, via the ‘is-checks’ keyword. 

#6 Coroutines Support – The components in Android belonging to the same application run in the same process and thread are typically referred to as the main thread and responsible for the UI. The CPU-intensive and Network I/O operations are termed as lengthy. When any of these operations starts, the respective calling thread gets blocked until the completion of the entire operation.

Java facilitates creation of multiple background threads to avoid complications on the main thread, while handling lengthy operations. The only limitation is the complexity of managing the multiple threads that may lead to more errors in the code.

Likely, Kotlin also provides the ability to create multiple threads. The better and most straightforward solution it provides as coroutines. Coroutines are stackless and they allow the developers to create code, suspend the code execution, and then resume it again later. This enables the non-blocking synchronous code to seem like the synchronous code. Hence, coroutines avoid having too many threads instead of a number of threads that the developer should handle later. Also, these threads are clear and concise than the solution Java provides. 

#7 Checked Exceptions – Kotlin skips checked exceptions. Therefore, it hardly requires catching or declaring exceptions. This can be a bit time-consuming and frustrating at one side, but on the other side it ensures robust coding and easy handling of errors. So, the checked exceptions support comprises it’s on advantages and disadvantages. Everything ultimately depends upon the priorities of the developers.

#8 Functional Programming – Lambda Expressions and Higher-Order Functions – As discussed earlier in this article, Kotlin comprises a mix of functional and object-oriented programming that behaves as a declarative style of programming and handles computations based on the mathematical functions. Lambda expressions and high-order functions come under some functional programming concepts.

High-order functions indicate that the functions should be sectioned as first-class. Therefore, the Kotlin allows the developers to make most out of diverse function types for representing functions. In simple words, operating functions in a diverse way is possible. 

Furthermore, using the Lambda expressions and or anonymous functions in Kotlin is also possible. These are regarded as a ‘functional literal’. Hence, it represents a function that seems undeclared and immediately passes as an expression.

In contrary, Java is mostly limited to the concept of object-oriented programming. However, Java developers have also been taking some steps towards functional programming as well. Java has introduced Lambda expressions in 2014 with its version Java 8, as a function that can be created without necessarily being related to a class. In fact, Java based lambda expressions can be passed as objects and executed on demand.

Java, after introducing lambda expressions, ultimately started supporting high-order functions. Java combines a function with a method and Java 8 has enabled the return of lambda from the methods.

#9 Primitive Types – In Java, ‘primitive type’ variables are not objects; they are data types of predefined Java. There are eight different primitive data types in Java such as byte, int, float, double, short, char, long, and Boolean.  Resultingly, these variables can hardly be an object represented from a class or a struct.

Even though primitive types do not fall into classes, the developers can use classes that comprise the value of the primitive type. However, they should indicate the things explicitly if they are doing this using Java. On the other hand, if you initiate a variable of a primitive type in Kotlin, it will automatically be regarded as an object.

#10 Public Fields – Public fields or non-private fields are available in Java. They can be quite convenient if an object’s callers need to modify as per the same object’s representation as it allows the developers to change the object’s representation without even adjusting the callers. The field can be public this way. Thus, the public AP remains unchanged and the program can attain a level of sustainable maintainability. On the other hand, Kotlin absolutely lacks public fields.

#11 Wildcard Types – Typically, a wildcard is a question mark in the code that suggests an unknown type of field, variable, or parameter. In contrast, Kotlin is free from providing wildcards. Instead, it comprises a declaration-site variance and type projections that serve as an alternative.

#12 Implicit Conversions – On one hand, Kotlin hardly provides support for implicit going conversions. Therefore, the smaller types are not possible to convert into the bigger types. To resolve this, Kotlin developers are needed to execute an explicit conversion for achieving the desired type conversion.

On the other hand, implicit conversions are perfectly supported by Java; thus, the developers are not at all needed to perform the explicit conversions.

Let’s summarize this difference easily in the table format so that it becomes more understandable.

Kotlin Vs. Java: Which is Better?

When talking about Kotlin and Java, both have their own strengths. Kotlin facilitates null safety and concise syntax. It is a modern development platform and is supported by Google for Android app development. However, Java comprises mature tools and libraries and a larger ecosystem. So, the term ‘better’ solely depends upon what your project needs. 

Now, when we have highlighted the benefits of both the development platforms, it is still harder to choose between both of them. Kotlin has now emerged as a new Android development language and has introduced some vital features of developing applications that has significantly simplified the life of the developers like extension functions, high-order functions, lambda expressions, NullPointerExceptions, and coroutines. These features have made the developers to affirm that yes, Kotlin is better than Java for efficient Android development and is anticipated by a number of mobile app development companies to dominate in the future as well. 

However, Java is still preferred for general-purpose programming. It is entirely understandable and excellent language for the developers.  It has been popular for years. But the usage of a language totally depends upon the comfort of the development team to deal with your projects.


Maneksoft – one of the fastest growing and reliable software and mobile app development service provider offers both the Kotlin as well as Java based Android development. On the serious note, developers at Manektech suggest that Kotlin has emerged as the best option at the moment for developing finest quality Android apps. The language is being sincerely adopted by many growing companies and businesses, but Java cannot be ignored. This debate over which language is better will go long; however, the company is capable of creating all types of finest quality apps on all development platforms and frameworks. It values its customers and delivers what is expected from them.

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