Kotlin Programming: The Big Nerd Ranch Guide, First Edition

For the More Curious: How Is Nullability Enforced?

Kotlin has strict patterns around nullness when compared to languages like Java. This is a boon when working exclusively in Kotlin, but how is this pattern implemented? Do Kotlin’s rules still protect you when interoperating with a less strict language like Java? Think back to the printPlayerStatus function from Chapter 4.

    fun printPlayerStatus(auraColor: String,
                          isBlessed: Boolean,
                          name: String,
                          healthStatus: String) {
        ...
    }

printPlayerStatus takes in parameters of Kotlin types String and Boolean.

If you are calling this function from Kotlin, then the function signature is clear – auraColor, name, and healthStatus must be of type String, which is not nullable, and isBlessed ...