The Elvis operator is used to provide a default value when the original variable is null – val name = nullableName ?: "Guest" ( Imagine doing that using null-checks.) 3. The variable currentCity will be null if any of user, address or city is null. For example, You can chain multiple safe calls like this – val currentCity: String? = user?.address?.city Safe call operator is even more powerful than you think. The lambda expression inside let is executed only if the variable nullableName is not null.
The most trivial way to work with nullable variables is to perform a null check before accessing a property or calling a method on them – val nullableName: String? = "John" Well, There are several ways of safely doing that in Kotlin. Working with Nullable TypesĪll right, It’s nice that Kotlin disallows method calls and property access on nullable variables to guard against NullPointerException errors. Since Kotlin knows beforehand which variable can be null and which cannot, It can detect and disallow calls which could result in NullPointerException at compile-time itself. Val upper = nullableGreeting.toUpperCase() // Compilation Error Kotlin disallows method calls and property access on nullable variables and thereby prevents many possible NullPointerExceptions.įor example, The following method access works because Kotlin knows that the variable greeting can never be null – val len = greeting.lengthīut the same method call won’t work with nullableGreeting variable – val len = nullableGreeting.length // Compilation Error We know that NullPointerException occurs when we try to call a method or access a property on a variable which is null. To allow null values, you have to declare a variable as nullable by appending a question mark in its type declaration – var nullableGreeting: String? = "Hello, World" So If you try to assign a null value to a regular variable, the compiler will throw an error – var greeting: String = "Hello, World" That means You have the ability to declare whether a variable can hold a null value or not.īy supporting nullability in the type system, the compiler can detect possible NullPointerException errors at compile time and reduce the possibility of having them thrown at runtime.Īll variables in Kotlin are non-nullable by default.
Kotlin supports nullability as part of its type System. Well, Enter Kotlin! Nullability and Nullable Types in Kotlin Wouldn’t it be nice if we could detect possible NullPointerException exception errors at compile time itself and guard against them?
NullPointerExceptions are Runtime Exceptions which are thrown by the program at runtime causing application failure and system crashes. If you have been programming in Java or any other language that has the concept of null reference then you must have heard about or experienced NullPointerException in your programs.
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