In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that cannot (non-null references). 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. Java provides its own implementations of this data structure as part of the collections framework.

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 Example Let’s implement a thread safe Stack in Java using Locks Stack is a common data structure and used often in Java. The only possible causes of an NPE in Kotlin are:Īn explicit call to throw NullPointerException(). This is a relatively minor update but does have a few new features. In Java this would be the equivalent of a NullPointerException, or an NPE for short. Version 20H2, called the Windows 10 October 2020 Update, is the most recent update to Windows 10. 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.

Null safety Nullable types and non-null types

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