Other issues caused by external Java code. For example, a piece of Java code might add null into a Kotlin MutableList, therefore requiring a MutableList for working with it. Nullability issues with generic types being used for Java interoperation. Usage of the !! operator that is described below.ĭata inconsistency with regard to initialization, such as when:Īn uninitialized this available in a constructor is passed and used somewhere (a 'leaking this').Ī superclass constructor calls an open member whose implementation in the derived class uses an uninitialized state.Īttempts to access a member of a null reference of a platform type The only possible causes of an NPE in Kotlin are:Īn explicit call to throw NullPointerException(). In Java this would be the equivalent of a NullPointerException, or an NPE for short. One of the most common pitfalls in many programming languages, including Java, is that accessing a member of a null reference will result in a null reference exception. Kotlin's type system is aimed at eliminating the danger of null references, also known as The Billion Dollar Mistake. In the next tutorial we will discuss about regular expression in Kotlin.Null safety Nullable types and non-null types Null safety is an important feature of Kotlin and it saves us from Null pointer exception. In this tutorial we discussed about Null safety in Kotlin. So, the !! operator should be avoided as much as possible. Let us understand them with examples: fun main() ') // Throws NullPointerException The compiler by default considers all variables as Non-Null Reference. These references are interpreted by compiler at the compile time. Non-Null Reference: These references can't hold null values. Nullable Reference: These references can hold null values. In Kotlin, the type system differentiates between two types of references: Let us discuss about the functionality given for it. Kotlin aims to remove NPE from our entire code. Kotlin tackles this problem by providing a mechanism to deal with NullPointerException. The NullPointerException can occur anywhere in the code due to negligence.

NullPointerException is considered as a billion dollar mistake as it leads to termination of program abruptly. Flutter Null Safety with example - dart migrate - flutter tutorial

Kotlin nullable types