Java v Kotlin

LiftOff LLC
3 min readMar 15, 2024

In the evolving landscape of programming languages, Java and Kotlin emerge as prominent figures, each with unique features and philosophies. Java, with its rich history and robust ecosystem, contrasts with Kotlin’s modern syntax and pragmatic design choices. This comparison delves into their differences and similarities, offering insights into their applicability in contemporary software development.

1. Null Safety and Optional


Java 8 introduced Optional as a way to explicitly deal with nullability, aiming to reduce NullPointerExceptions.

Optional<String> name = Optional.ofNullable(null);
name.ifPresent(System.out::println); // No output, avoids NullPointerException


Kotlin inherently addresses null safety through nullable types and safe calls, offering a built-in, seamless approach to avoiding null-related issues.

val name: String? = null
println(name?.length) // Prints "null", no risk of NullPointerException

2. Extension Functions

Java: Does not support extension functions natively; requires utility classes or patterns like the decorator to extend functionality.


fun String.exclaim() = this + "!"
println("Hi".exclaim()) // Hi!

Kotlin introduces extension functions, allowing developers to extend the functionality of classes without inheriting from them. This simplifies the code and enhances readability, a feature Java lacks.

3. Data Classes

Java: Java 16 introduced records, which simplifies the syntax but still more verbose compared to Kotlin.

public record Person(String name, int age) {}


data class Person(val name: String, val age: Int)

Kotlin’s data classes simplify the representation of data with minimal boilerplate code, automatically generating equals(), hashCode(), and toString() methods. Java’s records are a step towards this simplicity but Kotlin remains more concise.

4. Type Inference


var list = new ArrayList<String>(); // Type inference introduced in Java 10


val list = mutableListOf<String>()

Both languages support type inference, which allows the compiler to deduce variable types. Kotlin’s approach is more flexible and is applied more broadly across the language.

5. Coroutines for Asynchronous Programming


Utilizes CompletableFuture and frameworks like Reactor or RxJava for async programming.


suspend fun makeNetworkCall() {
// Efficiently handles asynchronous operations

Kotlin’s coroutines provide a lightweight way to handle asynchronous programming, simplifying complex operations compared to Java’s CompletableFuture and reactive libraries.

6. Checked Exceptions


try {
// Risky IO operations
} catch (IOException e) {

Kotlin: Kotlin does not have checked exceptions, offering a streamlined error handling approach.

Java’s checked exceptions enforce error handling but can make code verbose. Kotlin eliminates checked exceptions, reducing boilerplate and offering a more flexible error management strategy.

7. Smart Casts


Java requires explicit casting even after an instanceof

if (obj instanceof String) {
String str = (String) obj;


if (obj is String) {
println(obj.toUpperCase()) // Automatically casts obj to String

Kotlin smart casts reduce the need for explicit casting, enhancing code readability and safety, contrasting with Java’s manual casting approach.

8. String Templates


String name = "world";
System.out.println("Hello, " + name + "!");


val name = "world"
println("Hello, $name!")

Kotlin’s string templates simplify string concatenation, making code more readable and concise compared to Java’s approach of using the plus operator.

9. Immutability


final List<String> myList = new ArrayList<>();


val myList = listOf<String>()

While Java supports immutability through the final keyword, Kotlin’s val provides a more concise syntax and immutable collections by default, promoting a functional programming style.

10. Collection Filtering

Java: Java’s stream API introduced in Java 8 allows for functional-style operations on collections.

List<String> myList = Arrays.asList("a", "b", "c", "d");
List<String> filtered = -> s.equals("d")).collect(Collectors.toList());


val myList = listOf("a", "b", "c", "d")
val filtered = myList.filter { it == "d" }

Kotlin offers a more intuitive and concise way to work with collections, directly incorporating functional operations into the standard library, contrasting with Java’s verbose stream API.


While Java continues to evolve, incorporating features like type inference and records to reduce verbosity, Kotlin stands out for its modern syntax, null safety, and coroutines for asynchronous programming. Kotlin’s design choices, emphasizing conciseness, safety, and expressiveness, make it an attractive option for modern applications. However, Java’s robust ecosystem and ongoing improvements maintain its relevance in the software development world. The choice between Java and Kotlin often depends on project requirements, team expertise, and specific use cases.



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