Apr 5, 2023, Mobile

Kotlin vs Java – key features, pros, cons, and usage, p. 1

Marta Tomaszewska Android Developer
kotlin java comparison
Are you wondering whether to use Java or Kotlin for your next software development project? Both languages have their strengths and weaknesses, and deciding between them can be challenging.

In the first part of our blog post, we’ll compare Java and Kotlin and help you decide which language is the best fit for your needs. When it comes to software development, the choice of programming language can have a significant impact on the success of your project. Java and Kotlin are both popular languages that can be used for a wide range of applications, from mobile app development to web development and beyond.


Java is a widely used programming language that was first publicly released by Sun Microsystems in 1995. It was designed to be platform-independent, meaning that code written in Java can run on any platform with a Java Virtual Machine (JVM) installed. It is an object-oriented language that is based on the syntax of C++ and Smalltalk.

Java was initially named Oak, after a tree outside the office of James Gosling, one of its creators. However, this name was already taken, so the team had to come up with a new one. Gosling eventually settled on Java, inspired by his love for coffee and a type of beans grown on the island of Java.

One of Java’s main goals is “write once, run anywhere,” meaning that code written in Java can be compiled and run on any platform that supports the JVM. 

It’s known for its robustness, security, and reliability, which has made it a popular choice for enterprise applications and mission-critical systems. It has a large and active community of developers, and there are numerous frameworks, libraries, and tools available to help developers build Java applications more efficiently.

Some of the key features of Java

Object-oriented programming

In the realm of object-oriented programming, Java is often referred to as a pure object-oriented language due to its robust support for OOP principles. Java provides an extensive range of OOP features, such as encapsulation, abstraction, and inheritance.

Its programs are primarily built around objects, with all data and applications contained within their respective objects and classes. The language’s emphasis on objects is demonstrated by the fact that a program cannot be executed without using classes. Java includes a rich set of classes that can be further expanded and grouped into packages.


Java’s famous tagline “Write Once, Run Anywhere” (WORA) highlights its cross-platform capability. This means that Java programs can be developed on one operating system and run on any other operating system without any need for modifications to the code.

This feature offers significant advantages in terms of software development, as it reduces the need to create separate versions of the codebase for different platforms, resulting in lower development costs and faster time to market.

Java’s cross-platform compatibility is made possible by its bytecode, which is a platform-independent representation of compiled Java code. This bytecode can run on any device with a Java Virtual Machine (JVM), regardless of the underlying hardware or operating system.

Garbage collection

Java includes automatic memory management through its garbage collection system, which helps developers avoid many common memory management errors.


Programming languages like Java require developers to take necessary precautions to prevent malicious acts and viruses from causing harm to systems. In Java, access modifiers can be utilized to ensure memory usage is properly managed, thereby mitigating potential security risks. Additionally, Java’s built-in security measures prevent viruses from infiltrating applets, further enhancing its security features.

Virtual machines are used to execute programs, and Java ensures secure execution by providing a sandbox environment that isolates the program from the rest of the system. This sandbox environment ensures that even if an application is compromised, it will not harm the system it is running on.

Large standard library

Includes a large standard library of classes and methods, which makes it easy to perform many common tasks without having to write custom code.


To enable multithreaded processing, Java’s source code is divided into smaller, more manageable pieces that can be executed at the right time and in the right order. This approach ensures that the program runs efficiently and without conflicts, even when multiple threads are executing simultaneously.

Java’s multithreading capabilities enable programs to handle complex tasks and processes that would otherwise require significant amounts of time and system resources to complete. By executing multiple tasks concurrently, Java programs can complete operations more quickly, enhancing overall performance and user experience.

Simplified memory model

Java’s simplified memory model, which includes automatic memory management and standardized memory access semantics, makes it easier to write correct and efficient code.

Usage of Java

Java is most commonly used in backend systems for web applications, meaning it is responsible for everything “under the hood”. It can also be used for desktop software development (JavaFX) and game development (see LibGDX). Additionally, it runs on a Linux based system which allows for the creation of Android apps and games. Currently, Kotlin is the official language for Android, which runs on the same virtual machine as Java and is fully compatible with it.

Java is suitable for both small and large projects and is the preferred language in corporations and large companies. It is often used in banking systems.

Moreover, Java can even be used in embedded systems thanks to Oracle Java Embedded. Typical examples include SIM cards, VOIP phones, Blu-ray players, TV sets, electricity, heat or water consumption meters, health monitoring devices, industrial control systems, and countless other devices.

Java has been used to develop many popular applications, including the widely popular game Minecraft. Other notable apps developed using Java include:

  • Apache Lucene

  • Apache Hadoop

  • Eclipse

  • NetBeans

  • OpenOffice

  • Tomcat

  • Jenkins

These are just a few examples of the many applications developed using Java, highlighting its versatility and wide range of uses.

Advantages of Java

  • Java is designed to be platform-independent, meaning that code written in Java can run on any platform with a Java Virtual Machine (JVM) installed.

  • Java is an object-oriented language that is based on the syntax of C++ and Smalltalk. This makes it a powerful tool for building complex software systems.

  • Java has a large and active community of developers, which means that there are many resources available for learning and getting help with the language.

  • Java is known for its robustness, security, and reliability, which has made it a popular choice for enterprise applications and mission-critical systems.

  • Java’s simplified memory model, which includes automatic memory management and standardized memory access semantics, makes it easier to write correct and efficient code.

Disadvantages of Java

  • Java is sometimes criticized for its performance, especially when compared to lower-level languages like C++.

  • Java’s garbage collection system can sometimes result in higher memory usage, which can be a concern for memory-constrained applications.

  • Java can have a steep learning curve, especially for developers who are new to object-oriented programming or who are coming from languages with different syntax.

  • Because Java is a popular and constantly evolving language, there are different versions of Java that can sometimes have compatibility issues, which can be a concern for developers maintaining large codebases. Yet there is backward compatibility between JDKs.


Kotlin is a modern, statically-typed programming language that runs on the Java Virtual Machine (JVM) and can be used to develop applications for Android, web, desktop, and server-side platforms. It was developed by JetBrains, the company behind popular development tools such as IntelliJ IDEA, and was released in 2011. Kotlin is rapidly gaining popularity, especially in the Android development community, where it is seen as a more modern and productive alternative to Java. However, Kotlin is not limited to Android development and can be used for a wide range of applications, from server-side web development to desktop and mobile applications.

The name “Kotlin” comes from the name of Kotlin Island, which is located near St. Petersburg in Russia. JetBrains, the company responsible for the development of the language, is based in St. Petersburg, so this name was a natural choice.

Some of the key features of Kotlin

Interoperability with Java

This compatibility allows developers to easily incorporate Kotlin into existing Java projects, making it a popular choice among Java developers who want to explore new programming languages.

Kotlin is designed to work with Java libraries and tools and runs on the Java Virtual Machine (JVM), which means it can leverage Java’s wide range of capabilities and features. Additionally, Kotlin maintains backward compatibility with Java versions 6 and 7, ensuring that developers can use Kotlin in projects developed using older versions of Java.


Kotlin is designed to be a more concise language than Java, with features such as type inference, lambdas, and extension functions that allow developers to write less code while still achieving the same results.

Null safety

Aims to eliminate the risks associated with using null references in code, which is often referred to as “The Billion Dollar Mistake.” In Java, attempting to access a member of a null reference will result in a null reference exception. However, in Kotlin, code that assigns or returns a null value will not compile, thus mitigating the risk of null reference exceptions. This feature is widely regarded as one of Kotlin’s most valuable attributes.


Is strongly encouraged as a best practice when working with data structures. Immutable data structures cannot be modified after they are created, eliminating the possibility of unintended side effects caused by changes to shared data. This helps make Kotlin code more predictable and easier to reason about. Additionally, immutability promotes thread safety and can improve the performance of concurrent code, as multiple threads can access immutable data structures.
There are two keywords used to declare variables:

  • var is used to declare mutable variables, which means that their values can be reassigned after initialization.

  • val is used to declare immutable variables, which means that their values can not be changed after initialization.


Coroutines in Kotlin offer several benefits, including better performance and lower memory usage compared to traditional threading approaches. They also provide a simpler and more natural way to write code that involves multiple asynchronous operations, such as network requests or file I/O. Additionally, Kotlin’s coroutines are fully interoperable with Java’s CompletableFuture and RxJava, which means that developers can use them alongside existing Java-based libraries and frameworks.

Extension functions

This feature provides a flexible and powerful mechanism for extending the functionality of existing code, as it allows developers to add new methods to classes that were not originally designed for those methods.

Extension functions in Kotlin are defined outside of the class and can be called as if they were class instance methods, making them easy to use and integrate into existing code. This can be especially useful when working with third-party libraries or APIs, as it allows developers to add new functionality to those libraries without needing to modify their source code. extension functions can access public properties and functions of the class they are extending, but they cannot access private properties or functions.

Higher Order Functions

A higher-order function in Kotlin refers to a type of function that can either accept another function as a parameter or return a function as its result. This feature enables the use of anonymous functions or lambdas instead of traditional parameters like integers, strings, or arrays.

Lambdas are commonly used as parameters in Kotlin functions for their convenience and flexibility. By passing lambdas as arguments to higher-order functions, developers can write more concise and expressive code that is easier to read and maintain. The use of higher-order functions also allows for a more functional programming style, which is increasingly popular in modern software development.

Kotlin Multiplatform Project

It’s also worth mentioning that there is a project called “Kotlin Multiplatform” being developed. Thanks to it, it’s possible to write common code for the business logic of an application that will work on multiple platforms, such as Android, iOS, Windows, Linux, and macOS, and as a web application.

Usage of Kotlin

Since Google announced Kotlin as the recommended language for developing applications on their mobile operating system in 2019, many developers may associate Kotlin mainly with Android. However, it’s worth remembering that this is not the only use of Kotlin. The language also works well for creating server-side or desktop applications. Generally speaking, it can be used wherever Java can be used (as a fun fact, Kotlin was used in the development of the integrated development environment IntelliJ IDEA).

Wondering where Kotlin is most commonly used? Primarily, it’s the main programming language for Android, so it’s useful in mobile applications. In addition, it proves to be a very good solution for creating backend servers or desktop applications. The most popular companies that use Kotlin include:

  • Netflix

  • Uber

  • Amazon Web Services

  • Pinterest

  • Coursera

  • Trello

Advantages of Kotlin

  • Kotlin’s syntax is concise and easy to read, reducing the amount of code needed to achieve the same result in other languages.

  • Kotlin can be easily integrated with existing Java code, making it a practical choice for developers who have already invested in Java codebases.

  • Kotlin has null-safety built into the language, reducing the likelihood of NullPointerException errors.

  • Kotlin has improved type inference, which can help catch errors earlier in the development process.

  • Kotlin allows developers to add new functions to existing classes without modifying the class itself.

Disadvantages of Kotlin

  • Although Kotlin has a relatively easy-to-learn syntax, it still requires developers to learn a new language, which can be challenging.

  • Kotlin can be slower to compile than Java, which can affect development time.

  • Compared to Java, Kotlin has fewer resources and libraries available, which can make certain tasks more difficult.

  • Although many IDEs support Kotlin, some may not have the same level of support as they do for Java.

  • While Kotlin is widely used in Android development, it may not be the best choice for non-mobile applications.

Wrapping up

That’s all for now, but stay tuned for the second part of the article in which I will tackle the issue of Kotlin vs Java similarities and differences.