Digging into the source code of Kotlin's compiler, one can find various flavors of the nullability annotation that aims to achieve this. The way to leverage the existing null safety mechanism is by representing platform types as an actual Kotlin type (nullable or non-nullable). When we try to invoke Java code from Kotlin, null checks are relaxed due to platform types. The following mnemonic notation can be used to denote them: Hence, there is no syntax in the language to represent them. E.g.įrom the Kotlin compiler perspective, it is a type that can be nullable and non-nullable. if we try to declare a variable of a platform type, we will receive a compilation error. These types cannot be mentioned explicitly in the program, i.e.

Java's declarations are treated as platform ( flexible) types in Kotlin. In this post, we will focus on how to take advantage of null safety when invoking Java code.

Using an uninitialized this in a constructor (data inconsistency).

Invoking external Java code, which in turn can throw NPEs.

Else if the variable is set from outside the class, use lateinit. Nevertheless, we can still encounter NPEs by: If it’s normal for the type to be null during the logic, use nullable. Which means we can deal with null at compile time rather than bumping into a Null Pointer Exception. Every Kotlin class has as a superclass.The JVM already provides a safety net in the form of bytecode verification, buffer overflow, type safety, etc., but Kotlin took this to a step further and baked null safety right into the type system. AnyĪny in Kotlin is on the top of the hierarchy. Note that Nothing is a subtype of Unit, that's why the first compile but not the last one. Or, if you prefer, is the result value of any statement (for example println()). The Unit type in Kotlin is the equivalent to the void type in Java. We will look in detail at Unit, Nothing, and Any, and compare against their Java corresponding classes.įinally, we also consider null and how types ending with ? fit into these categories. To take full advantage of the Kotlin Type Hierarchy, it is essential to understand how these three special types work.

It is also quite close to the Java Type System, so the interoperability is excellent.ĥ Things You Will Like in Kotlin as a Java Developer One of the reasons is its Type Hierarchy, which is both very easy to work with and extremely powerful. For simple properties setting it to null is not a problem but for properties with a backing property, etc. It should be apparent, even to the casual reader of this blog, that I really like Kotlin as a language. 2) If it is null - something does happen: an assignment. String of pearls How to Take Advantage of Kotlin Special Types

Kotlin is null