Java vs. Kotlin: Comparing Two Modern JVM Languages

6 min readDec 7, 2023

Java is an incredibly popular and versatile programming language that is used in web, mobile, and desktop application development. On the other hand, Kotlin is a newer, more advanced version of Java, and it has a bunch of modern features that Java doesn’t have. However, if you are used to Java, there are several things you can miss in Kotlin.

In this article, we will compare the syntax, features, performance, and cost associated with developing programs in both languages so you can understand which language is suitable for your project.

Introduction

Java is a versatile, mature, platform-independent, general-purpose programming language that has maintained its prominence for more than two decades. Kotlin is a newer programming language inspired by Java, with a handful of modern features that help developers write programs in a more concise way.

Both languages are used in the development of a variety of applications. However, there are some scenarios where you may prefer one over the other, which we will discuss in a later part of this article. For example, Kotlin has an upper in Android application development while Java is still dominating the server-side, web, and desktop applications.

In fact, Kotlin was developed to address some of the limitations in Java, which has contributed to its growing popularity. Since it is fully interoperable with Java (you can use existing Java libraries, APIs, frameworks, and code and even mix both in one project), it also adds to the functionalities of Java.

Considering these factors, the debate among developers has consistently revolved around Java vs Kotlin. While no programming language can definitively claim superiority, a particular language may prove more suitable once your specific requirements become clear.

Let’s explore some key factors that deserve your attention to help you make an informed decision.

Syntax: Java vs. Kotlin

Kotlin is like a concise poem, while Java is like a verbose essay.

Kotlin is designed to support both object-oriented and functional programming paradigms, which allows developers to write code that is both expressive and concise. Additionally, Kotlin offers a more concise syntax.

Here is a simple program to calculate the sum in Java and Kotlin that compares the conciseness of the two languages:

In Java

public class JavaProgram {
public static void main(String[] args) {
int sum = 0;
for (int i = 0; i < 10; i++) {
sum += i;
}
System.out.println("The sum is: " + sum);
}
}

In Kotlin

fun main() {
var sum = 0
for (i in 0 until 10) {
sum += i
}
println("The sum is: $sum")
}

Both programs perform identical tasks, but it’s the Kotlin program that glides gracefully with a touch of readability. For example, in Kotlin’s for loop, it doesn’t just use the mundane “for" keyword and the mundane "i < 10" condition – it has "until" keyword, making the program more human readable.

In addition to this, there is a wealth of improvement Kotlin has to offer for Java developers, including a few of them, such as you don’t need to explicitly specify the data type, Kotlin’s function declaration is shorter, etc.

On the other hand, Java requires variables and expressions to be declared explicitly. Therefore, Java has a relatively verbose syntax, with many keywords and punctuation marks.

Kotlin is also a statically typed language, but it has a more concise syntax than Java. Kotlin uses type inference to automatically determine the types of variables and expressions, which can make code more readable and maintainable.

In terms of writing programs, Kotlin has the upper hand, and you can express the same functionality with less code in a concise way.

Comparison: Java vs. Kotlin

Features: Java vs. Kotlin

More specifically, Kotlin is a newer language with modern features compared to its counterpart, Java. They share many common features, but there are also several distinct features that developers often evaluate from their perspective.

Features such as Explicit nullability and Extension functions help developers write more reliable and maintainable codebases in Kotlin. On the other hand, Kotlin does not have the ternary operator, static members, checked exceptions, and protected features.

Let’s examine in detail the features comparison in Java and Kotlin.

Checked exceptions: Java requires developers to handle checked exceptions explicitly. This helps to prevent errors.
Higher-order functions: These functions can take other functions as arguments or return functions as results. This can be useful for writing more concise and reusable code.
Static members: Static members are members of a class that can be accessed without creating an instance of the class. This can be useful for sharing code and data.
Strictfp: The Strictfp keyword can be used to declare a method as having strict floating-point semantics. This can be useful for some specific tasks, but it can also make code less efficient.
Data classes: Data classes are a simple way to create immutable data classes. This can be useful for writing more concise and efficient code.
Ternary operator: Ternary operator is a shorthand way to write conditional expressions. This can be useful for writing more concise code.
Coroutines: Coroutines are a lightweight way to write asynchronous code. This can be useful for writing more responsive and efficient code.
Varargs: Varargs is a feature that allows a method to accept a variable number of arguments. This can be useful for writing more concise and flexible code.
Native methods: Native methods are methods that are implemented in a native language, such as C or C++. This can be useful for writing code that is more efficient, or that needs to interact with native code.
Extension functions: Extension functions can be added to existing classes without having to modify the classes themselves. This can be useful for adding new functionality to existing classes without having to make breaking changes.
Type inference: Type inference is a feature that allows Kotlin to infer the types of variables and expressions. This can make code more concise and easier to read.
Smart casts: Smart casts are a feature that allows Kotlin to cast variables to their inferred types automatically, making code more concise and easier to read.
Inline functions: Inline functions are functions that are expanded inline at the point of use. This can improve performance, but it can also make code more difficult to read.
Type aliases: Type aliases are a way to create new names for existing types. This can be useful for making code more concise and readable.
Null safety: Among these features, Null safety is a great addition to Kotlin, which saves time for developers as developers don’t need to deal with null NullPointerException. They are a significant problem in Java projects.

Performance: Kotlin vs. Java

They both have similar performance, as they are compiled to bytecode and run on the JVM. Kotlin may have a slight advantage over Java in certain cases. However, Java code is typically compiled faster than Kotlin, especially when using reflection.

On the other hand, Kotlin may outperform Java for small and simple programs, as some benchmarks have shown that Kotlin has better performance than Java in these cases. Additionally, Kotlin’s unique features, such as null safety and immutable data structures, can also contribute to the performance of Kotlin programs.

NullPointerException can reduce the number of runtime exceptions, resulting in improved performance of the application.

In summary, choose Java if you need to develop large and complex applications, as it is a mature language with robust resources. Kotlin is a newer language, but it is taking over Java for small application development due to its concise syntax and modern features.

Community Support: Java vs. Kotlin

Java

Java has been around for a long time and has a massive community. This translates into a wealth of resources, libraries, frameworks, and essential tools for developers. You can find solutions to almost any issues that you may encounter.

Additionally, Java has a great ecosystem of tools and IDEs, like Eclipse and IntelliJ IDEA, backed by a robust community of contributors.

Kotlin

Kotlin is relatively new, but its community is growing rapidly. You will also find many libraries and several frameworks available for Kotlin development, and support is available from Google and other companies. Kotlin’s official website, along with online communities like Stack Overflow and GitHub, provides ample resources for learning and troubleshooting.