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Differences Between Kotlin and Java

August 11, 2021

It has been quite a while since Kotlin came out, and it has been progressing nicely. Since it was made explicitly as an alternative to Java, Kotlin has normally been contrasted with Java in numerous aspects such as syntax among others.

Java is a programming language and a platform for computers. Most back-end projects, notably those involving big data and Android development, employ it as their server-side language.

Kotlin, on the other hand, is a free, open-source, statically typed programming language that mixes object-oriented and functional programming capabilities.

Kotlin was created with the JVM (Java Virtual Machine) and Android in mind. Priorities include interoperability, safety, clarity, and tools support.

In this article, we will look into the areas of specialization that make these two languages differ.

These areas are:

  1. Syntax comparison
  2. Lambda expressions
  3. Model classes
  4. Global variables
  5. Concurrency

Syntax comparison

Although these two languages are both used in application development, they have some differences in their syntax.

One clear difference is that the presence of semicolons at the end of a statement is enhanced in Java while in Kotlin semicolons are not needed.

Java example:

public class myClass
    public void Name(String Name){
        String Name = " ";
        System.out.println("My name is :" + Name );
public void age()
    int age = 30;
    System.out.println("I am " + age + "years old");
public static void main(string [] args)
    myClass my = new myClass();

Kotlin example:

class myClass
    fun FullName(firstName:string , lastName:String)
        var fullName = "$firstName $lastName"
        println("My name is  :$fullName")
fun age()
        var age : Int
        age = 30
        println("My age is : $age")
    fun main(args :Array<String>)
         myClass().FullName("Ben White")

From the code above, it is clear that Java has more lines of code compared to Kotlin. This comes about because Java enforces the concept of object-oriented programming in detail whereas Kotlin does not strictly enforce it.

Apart from the minor variations in syntactic patterns, Kotlin and Java are very similar. However, Kotlin is more versatile in some ways.

Expressions in Lambda

Lambda Expressions are simply anonymous functions that we can treat as values, pass them as arguments to methods, return them, and do whatever we can do with regular objects.

In Java, when implementing Lambda expressions, parenthesis is preferred, but if there is only one parameter, parenthesis is unnecessary.


parameter -> expression
(parameter a, parameter b) -> {code}

Java example:

interface Drawable{
    public void draw();

public class LambdaExpressionExample {
    public static void main(String[] args) {
        int height = 50;
           //lambda implementation
        Drawable d2 = () -> {
            System.out.println("Draw "+height);

In Kotlin, we use curly brackets to implement Lambda expressions.

Kotlin syntax:

val lambdaName : Type = { argumentList -> codeBody }

Kotlin example:

val square = { number: Int -> number * number }
val nine = square(3)

Even though the use of Lambda expressions minimizes the lines of code, code readability becomes a challenge.

However, in matters concerning what language to use in such a situation, Kotlin is still more preferred because it promotes the use of brackets to aid in readability.

Model classes

A model class represents a data object that can be used to transfer data in a Java program. It encapsulates direct access to object data and ensures that all data is obtained through getter methods.

To adhere to the encapsulation concept, properties in Java are defined as private. Java employs Getters and Setters to access these attributes, as well as the isEqual and toString methods as necessary:

public class Employee {
     private String name;
     private Integer age;
     // Default constructor
     public Employee() { }

     public void setName(String name) {
         this.name = name;

     public String getName() {
         return name;

     public void setAge(Integer age) {
         this.age = age;

     public Integer getAge() {
         return age;

In Kotlin, data classes serve the purpose of model classes. Data classes make it possible to access properties directly. They also have several built-in utility functions such as equals(), toString(), and copy().

//Kotlin data class
data class Student(var name: String = "", var age: Int = 0)

var Employee: Employee = Employee("Ben White", 30)

Data classes are one of the best things Kotlin offers. They are designed to cut down the amount of boilerplate code required for ordinary model classes.

Global Variables

A global variable can be seen and used throughout the application.

Because it is not contained as an object, the static keyword in Java is used to supply global variables at the start of the program’s execution. This indicates that it can be utilized without the need to build an object:

public class myClass {
   public static int global number = 19;
// it can be called without initializing the class

In Kotlin, the static keyword is replaced by a companion object, which is similar to a singleton. It enables you to have access to various features like extensions and interfaces:

class myClass {
    companion object {
        val globalNumber = 19


This refers to a programming language’s capacity to perform multiple tasks at once.

Java threads are mostly used to support concurrency. Making a thread in Java necessitates creating a class that extends the built-in Java thread class. The rest of its application should be uncomplicated.

// Creating a thread in Java by extending    //the Thread class
class MultithreadingDemo extends Thread
    public void run()
            // Displaying the thread that is running
            System.out.println ("Thread " +
                  Thread.currentThread().getId() +
                  " is running");
        catch (Exception e)
            // Throwing an exception
            System.out.println ("An exception is caught");
  // Main Class
public class Multithread
    public static void main(String[] args)
        int x = 30; // Number of threads
        for (int i = 0; i < x; i++)
            MultithreadingDemo object = new MultithreadingDemo();

In Kotlin, threads are also available but what is used instead is coroutines. Coroutines are lightweight threads that excel in short non-blocking tasks.

for (x in 1..500)
    GlobalScope.launch {

Learning curve

Both Kotlin and Java have major differences in their implementations of various concepts in application development. Despite these differences, Java still reigns supreme in the community aspect which makes it easier to learn and get help.


In this article, we have seen the differences between these two languages. However, Java takes the upper hand when it comes to the development of applications because it is easier to learn and implement.

Happy coding!

Peer Review Contributions by: Peter Kayere