This ensures that a NullPointerException doesn’t occur. If you want a variable to accept nulls, you have to mark the type with a ?: val x: Int? = null Compile-time checkīut, from that point on, the compiler will force you to check the null before doing anything with the variable. Therefore, this won’t compile: val x: Int = null Remember that in Kotlin all types are objects. This results in faster code execution and better performance compared to dynamically typed languages like Python and Ruby. That is, no variable, by default, can be set to null. Kotlin is a statically typed language, which means that it can perform type checks at compile-time. Nulls in Kotlin don’t exist until you say otherwise. Thanks to Kotlin, you’ll work in a much safer environment (even with Java libraries), which will minimize these problems. If you look at your bug manager, I’m sure that +90% of the errors you see are NullPointerException.

If you want to start today, I recommend you take a look at my free training, where you will have an hour and a half of content to know what are your next steps to become an expert in Kotlin. Nulls are one of the most error-prone points you get when you are coding with Java. Tony Hoare, the creator of the idea of nulls, calls itself “the billion dollar mistake”. It had taken me too long to write an article to one of the most important parts of Kotlin: the treatment of nullity.

Null check in kotlin