is there a trick to make overriden fields not null...

# announcements

[christophsturm]

is there a trick to make overriden fields not null? for example in my own RuntimeException subclasses i want message to be String and not String?.
actually, in this example the compiler could infere that message is not nullable for all subclasses of ApplicationException, or am I missing something?

open class ApplicationException(message: String, cause: Throwable?) : RuntimeException(message, cause)

[Edgars]

It's just a constructor parameter. The underlying getMessage() /`setMessage()` methods in RuntimeException can still return a nullable value or set the message to null. If your subclass overrides those methods, then you could make it work.

[Edgars]

open class FooException : RuntimeException() {
    override val message: String = super.message ?: "default message"
}

[Edgars]

Or take it from the constructor params

open class FooException(msg: String) : RuntimeException() {
    override val message: String = msg
}

[christophsturm]

hmm i can swear that I tried this: `

open class ApplicationException(override val message: String, cause: Throwable?) : RuntimeException(message, cause)

but it seems to work. thanks

[Edgars]

Or that, yeah.

[christophsturm]

i somehow thought that kotlin does not allow to change nullability when overriding methods

[Edgars]

You can't go from a non-null field to a nullable one. All nullable things can be non-null, but non-null things can't be nullable. 🙂