Kotlin Vs Java Comparison in 2024: Why Google Prefer Kotlin Over Java?

It is the ultimate battle of top mobile app development languages – Kotlin Vs Java. All the trouble began back in 2011 when Kotlin was introduced in the Android development world. Before the introduction of Kotlin, Java was eliminating all possible competitors with ease. Kotlin took an interesting approach to this challenge. With the support of Google and Jetbrains, Kotlin set out to replace the Java programming language by wrinkling out any of Java’s limitations and providing some additional features to the developers. Has it been successful in doing so? Do developers feel the need to abandon Java and switch to Kotlin entirely? Which is better for android app development – Kotlin or Java? These are some of the hot topics around these two popular programming languages. Let us understand their potential, challenges, limitations, and benefits to get a clearer idea of their capabilities.

Kotlin Vs Java – Android App Development

If we talk about Android App Development, Java and Android are like bread and butter; they are often paired together. One of the primary reasons behind this is also that Android SDK itself is written in Java. Java was originally built back in 1995 by Sun Microsystems Inc., which was acquired by Oracle Corporation back in 2010. In contrast, Kotlin was introduced to the world on July 22, 2011. It was a fairly new programming language, and Java had already marked its presence in the android app development niche. Kotlin was introduced as the preferred language for Android App developers during the Google I/O held back in May 2017. This stirred things up, and people started acknowledging Kotlin as a worthy competitor to Java.

What is Kotlin?

Kotlin is a general-purpose programming language developed by Jetbrains. General-purpose refers to Kotlin developers’ ability to share code data and logic with various web programs. This allows Kotlin to interact with Swift or XCode for iOS, Android Studio, and Kotlin for Android. Kotlin is a flexible programming language that can interact with various native environments.

What is JAVA?

Java is a class-based, object-oriented programming language designed to make use of the least implementation dependencies possible. It is also a general-purpose programming language to let Java developers – write once, run anywhere (WORA). This means if any platform has JVM (Java Virtual Machine), Java programs can run on those platforms – Windows, Linux, and Mac OS, and more.

Kotlin Vs Java – Pre-requisites

Suppose you are a developer or are looking for developers to hire for Java app development or hire Kotlin app developers. In that case, you should know the basic skills/languages a developer needs to know to work with Kotlin and Java.

Kotlin Architecture

Java Architecture

Pre-requisites of Kotlin

1. Basic understanding of Java
2. Exposure to any programming environment
3. Basic concepts clarity like – Syntax, commands, and variables

Pre-requisites of Java

1. Starting and using a command-line shell
2. Previous experience and understanding of C/C++
3. Basic concepts clarity like – Syntax, commands, and variables

Kotlin Vs Java – Benefits and Limitations

As previously discussed, Java has enjoyed an undisputed throne for more than two decades and still hasn’t lost much of its popularity as a programming language. In comparison, Kotlin has brought new development capabilities for Android development. It fixes many loopholes and limitations of Java and is a worthy competitor for the throne. Let us understand the advantages and limitations of both these programming languages over each other.

Benefits of Kotlin over Java

Conciseness

Kotlin has proven to be more concise compared to Java. By various estimates, it can be concluded that Kotlin reduces the number of lines of codes by 40 percent compared to Java, hence shrinking the codebase. This helps in leaving less space for bugs and errors, resulting in overall quality improvement.

Functional Programming Support

Java is an object-oriented program which is not a limitation, but Kotlin trumps Java here by giving their developers the choice between object-oriented programming and functional programming. Kotlin also has better function types built-in than Java’s Single Abstract Method, which can help developers troubleshoot problems a lot better.

Interoperability

One of the greatest advantages Kotlin has is that it is completely interoperable with Java. Using Java to Kotlin converter and integrating it into IntelliJ will provide a smooth transition to Java code. Kotlin also supports all Java libraries and compiles them into Java-compatible bytecode.

Supportive Community

Kotlin is comparatively a younger language, but it has developed quite a strong and supportive community despite that.

Fail – Fast System

Kotlin comes with a fail-fast system that helps in reducing bugs and avoiding errors while coding as much as possible. There are three dedicated library functions for this purpose – check, require, assert.

Limitations of Kotlin

Lack of Resources

Kotlin was released back in 2011, but its spurt of popularity only began a few years back. Hence it is not very easy to find experienced Kotlin developers to teach and lead your team.

Slow Compilation

The code compilation of Kotlin is slower than that of Java. Java, on average, is 17 percent faster in compiling clean builds. However, it covers up in incremental builds with no files or one isolated or core file changed by being at par with Java in terms of compilation speed (at times even faster).

Benefits of Java

Easy to Lean

Java is easier to learn compared to many programming languages available today. Hence it is easier to write, compile and debug with Java. It has a comprehendible and understandable syntax, making it a good starting point to learn to program. Besides, if you plan to use Kotlin, you need to have a basic background in Java too.

Platform Independent

One of the biggest advantages that Java has is the fact that it is platform-independent. Java compiler converts the source code to bytecode which is known as an ‘intermediate language. Bytecode is executable on any platform by using JVM.

Strong Community

Java naturally has a very strong community with one million+ repository on Github. Hence you can use thousands of different libraries and frameworks with Java and speed up the development process.

Limitations of Java

Verbosity

Java requires far more code than Kotlin or most programming languages there are. Due to this, there are many risks of bugs and errors in Java as compared to Kotlin.

Nullability Problems

NullPointersExceptions is the biggest headache for Java developers that use non-nullable variables. This can be a frustration for Java developers since null is used to denote the absence of value. For this, Java developers need to write a few extra lines of code to find a way around this issue. We will discuss this in greater detail in the ultimate showdown section of – Kotlin Vs Java.

Kotlin Vs Java  built Popular Apps

The Detailed Comparison on Kotlin Vs Java – The Showdown

So far, we have understood what both these programming languages are capable of and also discussed their limitations to an extent. Now that we know what both of them have to offer, we can get into more technical aspects of their functioning, operating and methodology. Let us compare Kotlin Vs Java on the most important aspects that a developer would look at before deciding which one to pursue –

1. Kotlin Vs Java – Syntax

In programming languages, the Syntax of any computer language is the set of rules that defines the structure of punctuations, symbols, and words. Without Syntax, you cannot understand the meaning or semantics of a language. Let us compare the Syntax between Kotlin and Java –

Kotlin Syntax –

class NameClass {
    fun FullName(firstName: String, lastName:String) {
        var fullName = "$firstName $lastName"
        println("My Name is : $fullName")
    }
}
fun Age() {
	var age : Int
    age = 21
    println("My age is: $age")
}
fun main(args: Array) {
    NameClass().FullName("John","Doe")
    Age()
}

Java Syntax –

public class HelloClass { 
	public void FullName(String firstName, String lastName) {
    	String fullName = firstName + " " + lastName;
		System.out.println("My name is : " + fullName); 
	}   
    	public void Age() { 
		int age = 21;
		System.out.println("My age is : " + age); 
	} 
	public static void main(String args[]) { 
		HelloClass hello = new HelloClass(); 
		hello.FullName("John","Doe");
        hello.Age();
	} 
}

If you look at both the syntaxes, you’ll realize the feel of the code isn’t significantly different; there are some small syntax changes here and there, especially with methods and classes. The real difference is seen where we realize Kotlin supports type inference where the variable type does not need to be declared and compared to Java; we don’t even need semicolons anymore.

Another observation can be that Java strictly enforces OOP (objective-oriented programming) as everything in Java’s snippet has to be contained inside a class. As opposed to this, Kotlin is flexible and not very strict with OOP. You can see this in the fun Age and fun main section of Kotlin, where they aren’t contained inside any class.

This also results in a lesser line of codes needed in Kotlin, whereas Java keeps a traditional approach of making everything lengthy, leading to higher chances of bugs and errors.

Verdict – Kotlin Vs Java – Syntax – Winner – Kotlin

2. Kotlin Vs Java –  Model Class

A model class is used to ‘model’ the data in your application. You can write a model class in your application that mirrors a database or a JSON. You can also use the objects of these classes as vessels to send/receive data. Let us compare the Model Class of both Kotlin and Java programming languages.

Kotlin Model Class

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

//Usage
var student: Student = Student("John Doe", 21)

Java Model Class

public class Student {

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

     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;
     }
}

Java declares all the properties as private as it follows the practice of encapsulation. For accessing these properties, Java uses Getters and Setters along with toString or isEqual string methods whenever needed.

Kotlin includes data classes for the special purpose of model classes. Using data classes allows properties to be directly accessed. They also come with various in-built utility methods such as equals(), toString() and copy().

Verdict – Kotlin Vs Java – Model Class – Winner – Kotlin

3. Kotlin Vs Java – Concurrency vs Coroutines

In a general context, concurrency is defined as the tendency for things to happen simultaneously in any system. In programming, concurrency means doing more than one thing at the same time. People often confuse concurrency with Parallelism. However, concurrency is when there are multiple sequences of operations running in overlapping periods.

Kotlin’s Coroutines

for (i in 1..1000)
    GlobalScope.launch {
        println(i)
    }

Here we are comparing Kotlin’s ‘coroutines’ to Java’s ‘concurrency’ not because Kotlin doesn’t support threads. It has threads, but it also has coroutines. Coroutines are lighter-weight threads that excel in short non-blocking tasks. Coroutines work differently than concurrencies as they are sequential, whereas concurrency threads can work in parallel. This helps remove a good chunk of boilerplate code from programming for Kotlin over Java.

Java’s Concurrency

// Java code for thread creation by extending 
// the Thread class 
class MultithreadingDemo extends Thread 
{ 
    public void run() 
    { 
        try
        { 
            // Displaying the thread that is running 
            System.out.println ("Thread " + 
                  Thread.currentThread().getId() + 
                  " is running"); 
  
        } 
        catch (Exception e) 
        { 
            // Throwing an exception 
            System.out.println ("Exception is caught"); 
        } 
    } 
} 
  
// Main Class 
public class Multithread 
{ 
    public static void main(String[] args) 
    { 
        int n = 8; // Number of threads 
        for (int i=0; i n; i++) 
        { 
            MultithreadingDemo object = new MultithreadingDemo(); 
            object.start(); 
        } 
    } 
} 

Java mostly relies on threads to support concurrency. For making a thread in Java, developers need to make a class that extends to the in-built Java thread class. The rest of it is pretty easy to understand. But the concept is fairly harder to grasp and test; however, threading is a long-used method, so that most developers would be comfortable with it.

Verdict – Kotlin Vs Java – Concurrency vs Coroutines – Winner – Kotlin

4. Kotlin Vs Java –  Extension Functions

Before we discuss this in greater lengths, this is a Kotlin exclusive feature not present in Java. We are mentioning this feature because it is one of the many loopholes that Java had that were fixed in Kotlin. Here is how the extension function looks like –

fun Int.plusOne(): Int {
	return this + 1
}

fun main(args: Array) {
    var number = 1
    var result = number.plusOne()
    println("Result is: $result")
}

As you can see, this feature allows Kotlin developers to have a new functionality without extending it to a class or needing to use any design patterns. It also allows developers to add more functionalities to any Kotlin variable classes.

Verdict – Kotlin Vs Java – Extension Functions – Winner – Kotlin

5. Kotlin Vs Java – Global Variables

Global variable in programming languages refers to any variable that has a global scope. This means this variable will be visible throughout your program unless you intentionally shadow it. The set of all global variables is known as the global state or global environment. Kotlin and Java both have support for such variables. Let us see how they both approach global variables in their code –

Kotlin’s companion object

class SomeClass {
    companion object {
        val globalNumber = 10
    }
}

//called exactly the same like usual
SomeClass.globalNumber

Java’s static variable

public class SomeClass {
	public static int globalNumber = 10;
}

//can be called without initializing the class
SomeClass.globalNumber;

As you can see, Java uses static keyword, which is also used in other programming languages like C++. It gets initialized at the start of any program’s execution. Java uses it to provide Java developers access to global variables since they are not contained as an Object. This allows Java developers to access the global variables anywhere without initializing the class as an object.

Whereas if you look at Kotlin, you’d realize it uses a different approach here. It removes the static keyword and replaces it with a companion object closely similar to a singleton. With companion object, you can implement fancy features such as interfacing and extensions.

Though Kotlin justifies not using static keyword by providing an alternative in the form of companion object, it is always better to have static keywords for global variables as they are more reliable. They also help the global variable codes be short and clean.

Verdict – Kotlin Vs Java – Global Variables – Winner – Java

6. Kotlin Vs Java – Null Handling

In any OOP language, null types have always been an adamant issue. The issue comes as Null Pointer Exception (NPE) when a developer tries to use the contents of a null value. This is one of those limitations that bother Java developers a lot, and Kotlin worked on correcting it as its type system is dedicated to eliminating NPE from the code. Let us have a look at how Java and Kotlin both approach Null Handling –

Kotlin’s Null Handling

//Kotlin uses null safety mechanism
var a: String = "abc" // Regular initialization means non-null by default
a = null // compilation error

//allowing null only if it is set Nullable
var b: String? = "abc" // can be set null
b = null // ok
print(b)

Java’s Null Handling

Object object = objServ.getObject();

//traditional approach of null checking
if(object!=null){
    System.out.println(object.getValue());
}

//Optional was introduced in Java 8 to further help with null values

//Optional nullable will allow null object
Optional<Object> objectOptional = Optional.ofNullable(objServ.getObject());

//Optional.of - throws NullPointerException if passed parameter is null
Optional<Object> objectNotNull = Optional.of(anotherObj);

if(objectOptional.isPresent()){
    Object object = objectOptional.get();
    System.out.println(object.getValue());
}

System.out.println(objectNotNull.getValue());

The issue with Java’s Null Handling is that it still uses the traditional checking system prone to human error. Kotlin provides null safety variables where the variable must be nullable if the value can be null. This helps you identify which variable can be null and helps you ensure that you implement the correct check. They came out with optional classes in Java 8 that improvised the null checking methods in Java.

However, if we were to choose one between the two, Kotlin takes this round easily as it requires you only to add a small amount of code for null checking.

Verdict – Kotlin Vs Java – Null Handling – Winner – Kotlin

7. Kotlin Vs Java – Popularity

If we consider popularity as a metric, it is always hard to define which programming language is better as there are many different aspects to consider. Java is naturally more mature than Kotlin in terms of duration it has been in the market and the job opportunities available and demand for Java developers in the market. Kotlin is relatively new, and is gaining considerable momentum in popularity in a few years but it still is leaps and bounds behind Java when it comes to becoming a globally known and practiced programming language.
Here is a Google Trends Statistics that clearly shows that JAVA is search much more as compared to Kotlin.

If we see the Stack Overflow Trends, it is observed that the demand of JAVA is declining and Kotlin demand is rising. However, still there is a huge difference margin between Java and Kotlin.

Verdict – Kotlin Vs Java – Popularity – Winner – Java

8. Kotlin Vs Java – Performance

Performance is one parameter that is always going to be opinionated. If we objectively look at Kotlin and Java, both of them compile to bytecode that runs on the JVM. Hence their memory performance is more or less the same.

Kotlin’s Performance

Kotlin is more functional than Java, as it has more features than Java. It is much more convenient to work on multithreading apps using Kotlin. As we discussed above, Kotlin’s coroutines take a better approach than Java’s concurrency.

Java’s Performance

Java has lesser extra features but that also makes it that much simpler. Lesser decorations also make Java faster than Kotlin. However, this additional speed for loss of some features is not significant enough to give Java a clear advantage here.

More or less, Kotlin and Java perform on the same scale, it depends whether you’re looking for more features or only need the basic services that Java has to offer.

Here are some performance tests and how Kotlin and Java rank on them in terms of execution time and memory usage –

Verdict – Kotlin Vs Java – Performance – Winner – Tie

9. Kotlin Vs Java – Salary and Job Opportunities

As per Stack Overflow in the US, Kotlin Developers earn around $54k on average while Java developers earn around $50k. The salary difference is not all that much to clearly declare one a clear winner when it comes to expected salary. However, naturally Java has better job opportunities as it has been in the market for long, and there is a higher demand for Java developers compared to Kotlin developers. However, this also means there’s as much competition with securing a good Java project as there are many experienced Java developers already in the field.

Wrapping it up!

We understood both programming languages in great depth. Also, We compared their basic fundamental differences for some of the most important functionalities that help a developer decide between the two programming languages. As you can see from the results, Kotlin steers as the clear winner in almost all aspects of Java. However, does this mean Kotlin is more preferred compared to Java? Not quite, as Java still holds the benefit of being older in the market. Hence, far more experienced Java developers don’t wish to switch to Kotlin despite its advantages over Java. So while Kotlin is a promising and upcoming programming language, it still has considerable time to grow to come at par with Java.