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The differences between Java and Kotlin

by Kate Winsley

Are you thinking about starting a career of an Android developer? May be, you are already an Android developer coding in Java who has just come across such a new programming language like Kotlin? In the both cases, you definitely should learn about the differences between these two coding tools and we hope our article will shed some light on this issue.

What is Java and what is Kotlin?

Let’s start our discussion of the differences between Java and Kotlin from describing the major features of the both programming languages.

Nowadays, Java which was launched in 1995 by Oracle is one of the most popular programming languages based on the object-oriented approach. Since the programmes created in Java are executed by Java Virtual Machine or JVM, they can be used on almost any platform. Undeniably, you have already noticed that Java programmes can also be executed within an Internet browser. This can be done with the use of a special Java plugin.

Today, the major usage of Java is back-end development as well as standalone programmes. Certainly, it is a major language for creating the Android applications since this operation system was developed in Java itself.

Kotlin is a relatively new programming language since it was created in 2011 by a team of coders working for IDE Jet Brains. The official release of this language took place in 2016. Kotlin is also based on JVM, however this language can be compiled to JavaScript. There is a full compatibility of Kotlin and Java stacks. In order to switch from Java to Kotlin, one will need to install a special Plugin.

So far, Kotlin is officially regarded as a supported Android development language and it is also a great choice for creating server-side apps.

The most crucial differences between Java and Kotlin

Beyond a shadow of a doubt, Java is still far more popular than Kotlin since it has been in the programming industry since the previous century. Yet, Kotlin is becoming more and more widespread, so you should definitely be aware of the key differences between these two languages used for the Android apps development.


The casting in Java is identified and performed by a programmer whereas Kotlin has a special option known as smart cast which has been developed with a view to identifying immutable types and performing casting by the compiler.

Checked exceptions

Java supports checked exceptions allowing the coder to handle errors allowing developers to create codes with good error handling.

Unfortunately, this option is not available in Kotlin which makes codes written in this language more prone to bugs. On the other hand, some developers might find coding without declaring and catching exceptions simpler.

Type inference

Java demands specifying the data type of a variable explicitly. This is not a case for Kotlin which is featured by type inference. Yet, if a programmer needs to specify a data type in Kotlin, it is also possible.

Functional programming

In Kotlin, a functional programming approach is present along with a procedural approach. As a result, you can use operator overloading, lambda functions, lazy evaluation, higher-order functions as well as many other useful options in Kotlin.

Functional programming in Java has been available since Java 8.

Compilation time

The compilation time of Java codes is up to 20% faster than the time of compilation of the codes written in Kotlin. Yet, when it comes to incremental built compilation, the time is almost the same for the both of languages.

Null values

Interestingly, Kotlin doesn’t support assignment of null values, however, there is a possibility of such a declaration with the use of special syntax. Without this special syntax which looks like value num: Int? = null, a Kotlin code with assigned null values will simply fail during the compile time. In case of Java, one can assign null values. Still, an attempt to access such values will lead to an exception which makes such an assignment counter-productive.

Data classes

Java requires declaration of various methods in order to create a class with data. Some of these methods are constructors, getters and setters. Kotlin makes it simpler for programmers. In this language, one has only to write a keyword data and the compiler will handle all the necessary methods and variables.

Do Kotlin and Java differ a lot?

Now, you can see the differences between Java and Kotlin. Although these languages do not have too many differences, some of them are rather crucial and demand special handling, especially when one is trying to switch from one language to another.

At the same time, there is great feature of the both languages. The thing is that they are interchangeable. This means that a code written in Java can be called inside a Kotlin code whereas a Kotlin code will work inside a Java code. Furthermore, once a code is compiled, it won’t be possible to find differences between classes written in these languages.

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