In Java, if you don't write null checks, methods may throw a NullPointerException: // Java int stringLength (String a) We say 'almost' because, even though intrinsic checks are generated, That means there's almost no runtime overhead for working with nullable types in Kotlin. All checks are performed at compile time. Kotlin prohibits such calls at compile time and thereby prevents lots of possible exceptions.Īt runtime, objects of nullable types and objects of non-nullable types are treated the same:Ī nullable type isn't a wrapper for a non-nullable type.

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. The most important difference between Kotlin's and Java's type systems is Kotlin's explicit support for nullable types. The second part, starting fromĬhecking the result of a function call, examines several specific cases to explain certain differences.

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. Nullability is the ability of a variable to hold a null value.

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