In Kotlin: `String` can never be null, `String?` c...

# announcements

[diesieben07]

In Kotlin: String can never be null, String? can. In Java String does not express any notion of whether or not it can be null.

[mersan]

I thought its something related to generics

[diesieben07]

So, in your example with the anyKotlin method, if the compiler infers String for T, it assumes "hey this method cannot return null now!". And since anyKotlin is written in Kotlin, the compiler "trusts" it (not sure of the exact rules here).
Inside anyKotlin, the compiler cannot insert any null checks after the Java method returns, since it does not know what T actually is, T might be String? in Kotlin, which then means that it can be null, so a null check would not be correct. So there cannot be any checks here.

[diesieben07]

If anyKotlin had a non-generic return type (or you did T : Any so that T can never be a nullable type) then the compiler could insert the null check.

[mersan]

thank you again for explaining it 🙂