If you are working in thriving fields like Android development, you should know the differences between two of the most used programming language — Kotlin vs. Java.

Both Kotlin and Java enjoy immense popularity as programming languages. Sometimes, it can create confusion when you have to pick one language for your android development project. Also, for those who want to learn a trending programming language, a lack of knowledge about them makes it hard for them to decide. 

To resolve these problems, we bring you the top differences between Kotlin and Java.

What Is Kotlin?

Kotlin is a new generation programming language that became open-sourced in 2012. This language aims to bring the best features of object-oriented programming and functional programming into one language.

what is Kotlin

This statically-typed language was designed to use in Android and JVM environments. However, you can use it on Javascript and native machine code via LLVM. Android creator Google announced in 2017 that they prefer Kotlin as the programming language for Android development.

Notable Features of Kotlin

  • Being a null-safe language, Kotlin can prevent errors usually caused by absent parameters that developers did not initialize correctly. 
  • Kotlin lets you implement your knowledge in Java. Hence, developers can code Android apps using both Java and Kotlin together. 
  • While working on this language, developers do not need to use “null” or “nil”. As a result, errors caused by missing types and parameters can be prevented.
  • Kotlin does not involve the use of unnecessary tokens or keywords. Hence, the code stays concise, and developers can easily read it.
  • Thanks to the automatic getters and setters generation, writing and reading the code becomes easier for the developers. 

What Is Java?

The simplest way to define Java is that it is an object-oriented programming language. It runs in JVM (Java Virtual Machine) and is usually used for backend or standalone app development.

what is Java

Running Java in a web browser required a Java applets plugin enabling. However, this is a tricky task and involves security risks. Luckily, you can run Java virtually on any OS.  

Moreover, the Android operating system is coded in Java. It makes it the go-to programming language for Android app development. 

Notable Features of Java

  • Unlike programming languages like C and C++, Java is compiled into platform-independent byte code. No matter which platform you run it on, the JVM can interpret the byte code all over the web.
  • The design of the Java language is so easy that one can learn it without much effort. Once you understand the basics of OOP Java, mastering it will only be a matter of time.
  • Since Java is an object-oriented language, developers can use it for extended projects. 
  • Java is a great option if you want to develop a virus-free and tamper-proof app. It even supports a public-key encryption-based authentication method. 
  • Being an architecture-neutral and platform-dependent language, Java is highly portable. You can run it on any platform of your choice.
  • If you compare Java with languages like C or C++, you will find it more dynamic than the rest. Apps designed with Java contain extensive run-time information that you can use to verify and resolve object accesses at run-time.

Kotlin and Java: Similarities

Kotlin and Java: Similarities

Before we compare Kotlin vs. Java, let’s look at the similarities between these two languages. 

  • The most prominent similarity is that they both compile to bytecode which gets executed by the JVM. 
  • Both Java and Kotlin support object-oriented programming.
  • Kotlin and Java have similar programming syntax, though they are not exactly the same. Still, a Java developer can understand Kotlin code without much difficulty.

Kotlin vs. Java: Differences

In this section, we have discussed the differences between Java and Kotlin.

Kotlin vs. Java: Differences

Null Safety

A NullPointerException occurs when you attempt to use a reference pointing to a null location in memory while referencing an object. These issues are almost impossible to prevent, and your app can crash when they occur.

Kotlin is a null-safe language that keeps you safe from this issue. A Kotlin variable is non-nullable by default that throws an error during compilation. Programmers who want a null variable need to define it explicitly. Hence, you will not see any Kotlin app crashing at run-time due to a null pointer because it detects any possible NullPointerExceptions at compile time.

Java programmers already know why people call NullPointerExceptions their mortal enemies. While working on this language, developers must regularly check for possible NullPointerExceptions and handle them to prevent them from occurring during run-time and initialization.


If you are talking about object-oriented programming, inheritance is one of its vital concepts. It means that the hierarchical class structure ensures that a child class naturally inherits the properties of a parent class.

Kotlin developers can use extension functions to achieve extended features without creating a new class. As a result, you need to deal with fewer code and classes with these extension functions.

Java users need to create a new child class if they want to extend the functionality of an existing class. This new child class not only inherits from the parent class but also offers space for extra functionality.

Type Inference

In Kotlin, there is no need to declare the variable type explicitly. Even if you do not pronounce it, Kotlin will assume the type.

In Java typing, you have to explicitly specify the type (string, float, etc.) while declaring a variable. Also, to use a defined primitive variable as a different primitive type, developers have to explicitly “cast” a variable to the other type. The name of this process is typecasting.

The smart casts feature is available on Kotlin. With this attribute, you rarely need to typecast your variables explicitly. The language allows you to use the “is-checks” keyword to make the compiler check for immutable values and perform implicit casting.

As you can see, using the smart casting and type inference of Kotlin, you can get rid of the manually typing and variable casting of Java.

Data Classes

To create a class in Java involves writing some boilerplate code. To store data in a class, you must perform tasks like defining the constructors, toString functions, getter and setter methods, the hashCode, etc. The whole thing is a hassle and can result in some silly syntax errors.

Data Classes

If you use Kotlin for your app project, you do not have to deal with any such problem. The Kotlin feature of incorporating data classes can fix this issue. For storing data in a class, developers need to define a class using the keyword “data.” This step will automatically produce the typical boilerplate code during compile time. 

This functionality significantly increases readability and eliminates unnecessary fluff from your code.

Checked Exceptions

Java supports checked exceptions, an unexpected event or error that occurs during the run-time of program execution. When these exceptions are checked at compile-time, they’re called checked exceptions.

On the flip side, Kotlin offers no support for checked exceptions. So, even with uncaught exceptions, this language doesn’t throw any errors at compile time. However, many programmers think removing checked exceptions from Kotlin was terrible. 

Functional Programming

Functional Programming

Functional programming is a feature that sets these two languages apart. This programming paradigm connects everything in a pure mathematical functions style. It reduces code redundancy, simplifies the solutions to math problems, and improves maintainability.

Kotlin involves functional methods, including operator overloading, lazy evaluation, and higher-order functions. So, if you have a functional programming background, you can easily learn Kotlin. However, no functional programming concept is available on Java.

Scalability and Reliability

While working on a development project, your language should be scalable and reliable. In these two aspects, both Kotlin and Java are similar. Also, these depend on how developers write the code using the language.

While Kotlin offers a null safety feature to make the code more reliable, Java can achieve the same result by checking and catching null pointer exceptions.

Memory Usage

Memory is another important performance metric to weigh in these two languages. Everyone wants their app to load and run faster, which means lower memory usage that supports fast program execution.

In this aspect, Kotlin is lagging behind Java. If you think that high memory usage can hamper your app’s user experience, you should use Java.


Compared to Java, Kotlin is easier to read because of its null pointer safety feature and data classes. Besides having better readability, Kotlin comes with a concise code where you can easily understand the core logic and find bugs.

Learning Curve and Adaptability 

Java is one of the oldest languages that has been around for a long time. The reason is simple: it is comparatively easy to learn and master for any wannabe or pro programmer. Moreover, teachers often use Java to teach object-oriented programming concepts to their students.

Kotlin is also an easy-to-learn language. Since it is interoperable with Java, people find it easy to adopt. Developers with Java projects can add functionality using Kotlin code without migrating their entire project. Therefore, Java and Kotlin developers can seamlessly collaborate.

Documentation and Community

Java boasts a huge developer community because of its presence in the development arena for a long time. Therefore, you are more likely to find a resolution to your problem from the vast and helpful Java community.

Though Kotlin has comparatively fewer developers in its community, the adoption has increased since the announcement from Google.

In the following table, we have made head to head comparison between Java and Kotlin.

Null SafetyIt comes with the null-safe featureThe null-safe feature is not available in Java
InheritanceDoes not need to create a new class child for extended functionalitiesWe need to create a new class child for extended functionalities
Type InferenceExplicit declaration of variable type is not neededRequires explicit declaration of variable type
Data ClassesCan easily incorporate data classesCareful creation of data classes is needed
Checked ExceptionsDoes not offer support for Checked ExceptionsOffers support for Checked Exceptions
Functional ProgrammingAvailable in KotlinUnavailable in Java
ReliabilityNull safety featureNull pointer exceptions feature
Memory UsageUse more memory spaceLess memory usage that facilitates quick app load
ReadabilityCode is concise and easy to readIt comes with less readability than Kotlin
Learning Curve and Adaptability Easy to learn and adoptSuper-easy to learn and implement
Documentation & CommunityHas a growing communityIt has a huge community

Is Kotlin Replacing Java in Android Development?

As you already know, Google has taken a Kotlin-first approach to Android development and recommends others to develop such apps with Kotlin. Speaking of Android Jetpack libraries, most of them are either written in Kotlin or support its features.

Is Kotlin Replacing Java in Android Development

On the other hand, Google still offers 100% support to Java for Android development. If you look into the existing Android apps, most are built with a combination of Java and Kotlin code. Also, there is not the faintest possibility that Android will stop supporting Java soon. 

If you are wondering whether Kotlin will replace Java for Android development, the answer is no. Not only Android SDK is written mostly in Java, most of the Android apps you use today include Java. Moreover, the Android OS is built upon JVM. So, shifting from Java to Kotlin would mean a major transformation in the Android ecosystem.

The above discussion made it clear that Kotlin will not completely replace Java. Due to Google’s Kotlin first approach, it might lose some market share to Kotlin within the Android ecosystem. Nevertheless, Java will remain a popular programming language in the world.

Wrapping Up

Every project manager should know the key factors of a language that can determine the success of app development. After going through this post, they will be able to understand the differences between Kotlin and Java and find out which one suits their requirements for developing powerful Android apps.

People who want to learn a programming language for a career switch or start their career as a developer will also get benefitted from this post. When it comes to learning, it is better to learn Java first and then Kotlin. For Java, you can try any of these online courses.