99. Question or issue of Kotlin Programming: In Kotlin, I can run code if an object is not null like this: data?.let { ... // execute this block if not null } but how can I execute a block of code if the object is null? There’s no point in optimizing code when comparing to null explicitly. Exceptions. If the property is always accessed from the same thread, we will never have multi-threading issues. Motivation. One of them is safe call. Java actually has a dedicated package for concurrency: java.util.concurrency. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). These functions give Kotli… 2. Annotations. Let’s start with the representation. 98. The == operator will call the equals function as long as the item on the left isn’t null. The rest of you might still wonder why the null check “does not work” or why the message says the property “could be changed by this time”? 101. The language uses plain old null. Now, without the support of static methods and ternary operator, you will face some troubles during the time of development. That’s why you don’t need the extra null check. If it is, it does a referential check of the right item for null. Follow. 1: Just use […] b : c can also be expressed like this: b.takeIf { a } ? This is the old pattern that we use in every other language, checking the variable if its null or not. Otherwise, it’ll return the default value specified to the right of the ? If you really don’t care about the absolute correctness or you just want to get rid of the compiler error, you can create a local variable referencing the property first: This compiles and runs as you would expect since variable name is only visible to the current thread and therefore the value is guaranteed to be non-null inside the null check. 0. : defaultValue. a local property which can’t be altered between the check and the utilization or a member ‘val’ which has a backing field and is not overridable), else it may happen that ‘nullableVariable’ changes to null after the check. Tagged with kotlin, android, programming. Maven Dependency. Here, the smart-cast is used, because now this is converted to a non-null type after the check. Note that, since throw and return are expressions in Kotlin, they can also be used on the right-hand side of the Elvis operator. Please login or register to answer this question. From the console output we can see the null check just cannot guarantee name won't be null when you access it exactly as what IDE tries to warn you. In this article, we’ll be looking at the null safety features built into the Kotlin language. In plain terms, if a string isn't a null and isEmpty() returns false, it's not Submitted by IncludeHelp, on April 27, 2020 . It is a variant of the ternary operator but for null-safety checking. Yes the first solution is simply just put !! If you are interested in the concurrency topic, Java Concurrency in Practice is a very good book to read. I am not going to cover all of them here. Originally published at: https://ask.ericlin.info/post/011-kotlin-stuff-null-checks-on-nullable-properties/. It returns the operand if it’s not null. ... Returns true if this nullable char sequence is either null or empty or consists solely of whitespace characters. It is fancily called the null-coalescing operator. For example framework only calls onStart() and onStop() on main (UI) thread, so you can feel confident to access private properties if the property is only accessed by those lifecycle methods. ... 1.0. fun Double. Ternary Operator Support: Java has the availability of this support that helps in reducing the length of the code. You might think that’s a stupid idea, but it is actually a legit solution when you can limit “how your property is accessed”. 101. Since Kotlin doesn’t have any information about the nullability of a type declared in Java, It relaxes compile-time null checks for these types. There are various ways of null checking in Kotlin. https://ask.ericlin.info/post/011-kotlin-stuff-null-checks-on-nullable-properties/, Building complex screens in a RecyclerView with Epoxy. The rest of you might still wonder why the null check “does not work” or why the message says the property “could be changed by this time”? 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