However if the compiler can prove that a call is safe, e.g.

The compiler prevents us from calling hello() with String? due to incompatible type. However we explicitly declare maybeStr as String? type (nullable String). Function hello() accepts String so hello(str) is fine. In the syntax layer each type T has a super type T? that allows null. We get NullPointerException-free code and no runtime overhead due to extra Option wrapper. References that can be null have different type, thus null-safety is encoded in the type system and enforced only during compilation.

Scala is first to adopt systematic, type safe Option monad (Java 8 will have Optional as well!) Idiomatic Scala code should not contain nulls but when interoperating with Java you must sometimes wrap nullable values.

Clojure renames null to nil, additionally treating it as false in boolean expressions.

Groovy has similar background but adds some syntactic sugar, namely Elvis Operator ( ?:) and Safe Navigation Operator ( ?.).

If it’s not a primitive, every single field, parameter or return value can be null.

Java doesn’t go much further than C - every reference (“pointer”) can be null, whether you like it or not.

There are at least couple of approaches to null handling in JVM languages: It has some good documentation so today I will focus on a tiny part of it - null safety. You might ask that if user’s address can be null then why the heck aren’t you returning an Optional instead of plain Address from getAddress() method?Īnd, You’re right! Let’s correct that, let’s now assume that getAddress() returns Optional.Kotlin is a statically typed JVM language developed by Jetbrains. Let’s consider the above map() example again.

Otherwise, it returns an Optional containing user’s address.

user is present but getAdderess() returns null.

In the above example, map() method returns an empty Optional in the following cases.

equalsIgnoreCase ( 'India' ) ) // Print, if country is India map ( User :: getAddress ) // filter address from India Optional indianAddressOptional = addressOptional. Extract User's address using map() method.

Kotlin optional to nullable