In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that cannot (non-null references). Kotlins type system is aimed at eliminating the danger of null references, also known as The Billion Dollar Mistake. ![]() Other issues caused by external Java code. Null safety Nullable types and non-null types. Kotlin provides us with another operator and converts any value to a non-null type and if the value found is null it throws an exception. For example, a piece of Java code might add null into a Kotlin MutableList, therefore requiring a MutableList for working with it. We can use the if-else expression to explicitly check for nullable. Nullability issues with generic types being used for Java interoperation. Let’s look at the different ways how we can handle null references safely in Kotlin. 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 So when we need to access value of a, then we need to perform safety check, whether it contains value or not. 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. A nullable type is a variation of an existing type, and can contain a null value. Null safety Nullable types and non-null types Default Kotlin types cannot contain null values.
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