Difference between Java and Kotlin - Developer view

Java is an object-oriented programming language. Programs or applications developed in Java will execute in a JVM (Java virtual machine ) by which we can run the same program on multiple platforms and systems/devices etc. Kotlin is a new programming language, which handles some modern features. Kotlin is also a statically typed programming language. Kotlin is a good choice for developing server-side applications, allows users to write concise and expressive code.

Kotlin is the modern programming language solution for Android. There are a few things that make Kotlin a great fit for Android:

-Compatibility: It’s compatible with JDK 6, so older devices aren’t left behind.

-Performance: It’s on par with Java.

-Interoperability: It’s 100% interoperable with Java including annotations.

-Footprint: The runtime library for Kotlin is tiny.

-Compilation Time: There’s a little overhead on clean builds but it’s way faster with incremental builds.

-Learning Curve: It’s easy to learn, especially for people used to modern languages. The Java to Kotlin converter in IntelliJ and Android Studio makes it even easier. You can also use a mix of Kotlin and Java in a project, so take your time learning Kotlin and add it in when you feel comfortable.

Working With Java and Kotlin Together

One of the most amazing qualities of Kotlin is that it can coexist with Java. Java code can call Kotlin code and vice versa. You might not even notice that you’re calling code in another language!

Java vs Kotlin

Declaring Variables

Declaring variables in Kotlin is simple and clear. Here are some variable declarations you’ll use often:.

var item = "house".

val points = 35.

var car: String = "BMW".

You can’t later reassign variables that you declare with val. Doing so triggers a compiler error. But you can with var. This is the difference between the two.This way of declaring variables is similar to Java’s final.

Null Safety

In Java, NullPointerExceptions causes huge frustration for developers. It allows users to assign null to any variables but while accessing an object reference having null value raises a null pointer exception which user needs to handle.

In Kotlin, By default, all types of variables are non-null able (i.e. we can’t assign null values to any type of variables/objects). If we try to assign or return null values, Kotlin code will fail during compile-time.

Nullable Types and Non-Null Types

Kotlin has nullable and non-null types. If you don’t declare a variable as nullable, you can’t assign it a null value. The compiler enforces this, making it harder to unintentionally crash your app.In contrast to Java, all variables must be initialized at the point of declaration, in a constructor or in a init, except lateinit var.

Safe Calls

To access a property or method on a nullable variable in Java, you would first do a null check.

if (shareActionProvider != null) {



With Kotlin, you can simplify the above expression with the use of the safe call operator ?.. The property or method is only called when the nullable variable is not null.


Here, setShareIntent is only called when the shareActionProvider property is not null.

Type Inference

Kotlin also supports type inference. This means the compiler can deduce variable types from the initializer. You can still declare the type if you want or if the compiler can’t infer it. For example, the types of the imageUrlBase and imageURL variables are inferred from their initializers.

private val imageUrlBase = "http://covers.openlibrary.org/b/id/"

private var imageURL = ""

The compiler tracks the inferred type of each variable, each as a String. Any values assigned after that to the variable must also be of that String type. For numbers, you need to make the type of variable clear to the compiler.

var longVar = 0L

var floatVar = 0.0f

var doubleVar = 0.0

var integerVar = 0

In Java, we need to specify a type of each variable explicitly while declaring. In Kotlin, we don’t need to specify the type of each variable explicitly based on assignment it will handle. If we want to specify explicitly we can do.

Extension Functions

In Java, If we want to extend the functionality of existing class we need to create a new class and inherit the parent class. So Extension functions are not available in Java

Kotlin provides developers the ability to extend an existing class with new functionality. We can create extend functions by prefixing the name of a class to name of the new function.

Coroutines Support

In Java, whenever if we initiate a long-running network I/0 or CPU Intensive operations, the corresponding thread will be blocked. As Android is a single-threaded by default. Java provides the ability to create multiple threads in the background and run but managing them is a complex task.

In Kotlin, We can create multiple threads to run these long-running intensive operations but we have coroutines support, which will suspend execution at a certain point without blocking threads while executing long-running intensive operations.

Data classes

In Java, suppose we need to have a class which needs to hold data but nothing else. For this we need to define constructors, variables to store data, getter and setter methods, hashcode(), toString(), and equals() functions

In Kotlin, If we need to have classes which need to hold data we can declare a class with keyword “data” in the class definition then the compiler will take care of all of this work such as creating constructors, getter, setter methods for different fields.

No checked exceptions

In Java, We have checked exceptions support which makes developers declare and catch the exception which ultimately leads to robust code with good error handling.

In Kotlin, we don’t have checked exceptions. So developers don’t need to declare or catch the exceptions, which have advantages and disadvantages.

Smart casts

In Java, We need to check the type of variables and cast according to our operation.

In Kotlin, smart casts will handle these casting checks with keyword “is-checks” which will check for immutable values and performs implicit casting.

Functional Programming

Java doesn’t have functional programming support till Java 8 but while developing Android applications it supports the only subset of Java 8 features.

Kotlin is a mix of procedural and functional programming language which consists of many useful methods such as lambda, operator overloading, higher-order functions, and lazy evaluation etc.

Finally, its an overview of comparison Between Java vs Kotlin. I hope you will have a better understanding of these Java vs Kotlin languages after reading this Java vs Kotlin article. In my view, we can proceed with Kotlin for Android application development without worrying about the compilation time even though Java has few advantages over Kotlin.