Check null kotlin10/22/2023 ![]() ![]() How Kotlin processes types from Java code. The first part of this guide covers the most important difference – support for nullable types in Kotlin and It will help you migrate from Java to Kotlin and write your code in authentic Kotlin style. This guide covers differences between Java's and Kotlin's approaches to handling possibly nullable variables. There are many ways to write code in order to minimize the probability of receiving null pointer exceptions. When a variable contains null, an attempt to dereference the variable leads to a NullPointerException. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that cannot (non-null references).Nullability is the ability of a variable to hold a null value. 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. ![]() Null safety Nullable types and non-null types ![]()
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