If a variable can be null, it's not safe to call a method on the variable because this can cause a NullPointerException. It is a way to indicate which variables can possibly hold a null value. For example the following codeįun main() class Person(var name: String = '', var surname: String = '')īut, in general, the use of !! operator it’s dangerous because expose our code to possible NullPointerException. The most important difference between Kotlin's and Java's type systems is Kotlin's explicit support for nullable types.

The ?: operator, also known as Elvis operator, it’s like an if else operator.

operator, also known as Safe calls, it’s used for calling a property, or a method, if and only if the field is not null.

The !! operator mean that we assert that the property will never be null.

In case if variable is null - you just assign null to it, so nothing changed.

Kotlin wayīefore explain how Kotlin is null safe we have to know some operators: In case if its not null - you assign null to this variable. This exception is thrown because we have initialized p1 with null and then we try to call a toString() method on null object. The code is syntactically correct and the compiler do not throw no kind of error at compile time, but what it happens if we try to run it? At runtime we have the exception NullPointerException.

Kotlin is not null