Why Kotlin



Kotlin is more secure than Java, mainly due to two language features

Null safety

The following code is not possible:

Variables in Kotlin are not nullable unless explicitely stated. How do we prevent a compilation error in the above piece of code?


Add a "?" to the value type to allow this:

But if you want to do something with those nullable values, you have to check for null: (Using the ?. operator. This is the "null safe dot operator", or "safe call operator").

==> Before running the snippet further down: what do you think is displayed?

See for more examples. If you are familier with freemarker you might recognise similarites:

Emphasis on Immutabilty

Shared mutable state is the root of all evil

Kotlin has one main constructs to prevent shared mutable state:

val vs var keyword

This code fails, because it reassigns to a val, you would have to change above code to a var.

This also works with java, using the "final" keyword

But there are some issues with the final keyword, mainly that it is ambigous: it is both used to declare variables immutable and to put constraints on inheritance. Furthermore you always have to ask yourself if you really want to use a var in Kotlin, while in Java you have to not forget the final keyword

Create your playground on
This playground was created on, our hands-on, knowledge-sharing platform for developers.
Go to
codingame x discord
Join the CodinGame community on Discord to chat about puzzle contributions, challenges, streams, blog articles - all that good stuff!
Online Participants