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Is Java still worth to learn instead of Kotlin?

Learning both languages will provide you with a broader skill set and increase your versatility as an Android developer.

If you want to learn Android development, both Java and Kotlin are valuable languages to consider. Java has been the traditional language for Android development and has a large codebase and community support. However, since May 2017, when Google announced official support for Kotlin as an Android development language, Kotlin has gained popularity rapidly.

Kotlin is the official first language for Android Development. I personally advise to learn Kotlin for Android Development, and besides that learn Java as Data Structures and Algorithms practices. Java is not dead for Android, since a lot of older projects are still written in Java, but new code mostly is written in Kotlin, – Reddit.

Here are some factors to consider when deciding between Java and Kotlin for Android development:

  1. Industry Adoption: Java has been around for a long time and has an extensive codebase in the Android ecosystem. Many existing projects and libraries are written in Java. However, Kotlin has gained significant adoption and is now considered the preferred language for Android development by many developers and organizations. The majority of new Android projects are being written in Kotlin.
  2. Language Features: Kotlin is designed to be more expressive, concise, and null-safe compared to Java. It provides features like extension functions, data classes, smart casts, coroutines, and more. These features can enhance your productivity and help you write cleaner and safer code. Java has also evolved over time, and recent versions (Java 8 and later) introduced several improvements, but Kotlin generally offers more modern language features out of the box.
  3. Learning Curve: If you already have experience with Java, transitioning to Kotlin should not be too difficult. Kotlin is fully interoperable with Java, allowing you to mix both languages in the same project. The Kotlin documentation and learning resources are abundant, and the language itself is designed to be easy to read and understand. Java has a vast amount of learning resources and community support due to its long-standing presence in the industry.
  4. Community and Support: Both Java and Kotlin have active developer communities. You can find numerous tutorials, sample code, libraries, and forums dedicated to both languages. Kotlin has gained substantial community support and has become the preferred choice for many Android developers, but Java’s community remains robust and vast.

Here are examples of code for a simple feature in both Java and Kotlin. Let’s consider a feature that calculates the factorial of a given number.

Java code:

public class FactorialCalculator {
    public static int calculateFactorial(int number) {
        if (number < 0) {
            throw new IllegalArgumentException("Number cannot be negative.");

        int factorial = 1;
        for (int i = 1; i <= number; i++) {
            factorial *= i;

        return factorial;

    public static void main(String[] args) {
        int number = 5;
        int factorial = calculateFactorial(number);
        System.out.println("Factorial of " + number + " is: " + factorial);

Kotlin example:

object FactorialCalculator {
    fun calculateFactorial(number: Int): Int {
        require(number >= 0) { "Number cannot be negative." }

        var factorial = 1
        for (i in 1..number) {
            factorial *= i

        return factorial

fun main() {
    val number = 5
    val factorial = FactorialCalculator.calculateFactorial(number)
    println("Factorial of $number is: $factorial")

These examples demonstrate how the factorial calculation can be done in both Java and Kotlin. Notice that the Kotlin version uses the object keyword to define a singleton object that contains the factorial calculation function. In Kotlin, functions can be defined outside of classes, allowing more flexibility.

Both examples take an input number and calculate its factorial using a loop. The Java example uses a traditional for loop, while the Kotlin example uses a range expression (1..number) to iterate over the numbers.

In terms of functionality, the Java and Kotlin code achieve the same result. However, you can observe the syntactical differences between the two languages, such as the null safety and type inference in Kotlin.

From a programming language design concept POV you should learn basic Java 9 syntax first, it should only take you a few hours, if it takes you longer, then it is likely better that you started with Java rather than Kotlin in the first place.

Kotlin IS nicer than Java 9 (later Java versions start to address Java’s issues, but 9 is the last one really supported by Android, for historical reasons), but Kotlin is honestly a more complex language for beginners IMHO.

People who know Java and have used it for a long time like Kotlin because of named parameters, parameter defaults, (those 2 are way more important than null handling IMHO too), and first class functions….etc…

I think Kotlin as a first language might actually be more complex for many beginners than others realize (I teach beginner OOP at my local univ, and we still teach Java, because of these above reasons).

Kotlin or Java?

Considering the current trend and the advantages Kotlin brings, it is recommended to learn Kotlin for Android development. However, understanding Java is still valuable as you may come across Java code in existing projects or libraries. Learning both languages will provide you with a broader skill set and increase your versatility as an Android developer.