Why is this Kotlin class property not public?

Question

I've got an app that is regularly using classes written in Kotlin which are accessed by other classes and their methods written in Java.

I had the following class in Java:

public class MyDataClass {
    public String color;
    public String action;
}

I've decided to move it to Kotlin:

class MyDataClass {
    var color: String = ""
    var action: String = ""
}

Upon recompiling, I'm now getting the following error message:

/myPath/MyApp.java:[93,20] color has private access in myapp.command.MyDataClass

I get a similar error for action.

Per the Kotlin reference, the default visibility modifier for class and properties (and a bunch of other things) is public.

Why are these properties being treated as private?

Brunt

Because it's a private field with a public getter and a public setter. You cannot access fields directly in Kotlin, everything is properties. – Recaption

Answer 1

Because it's a private field with a public getter and a public setter. You cannot access fields directly in Kotlin, everything is properties.

Refer to: https://kotlinlang.org/docs/reference/properties.html#backing-fields

Recaption

Thanks. What do you mean by "everything is properties"? – Brunt

If you declare the var something: String, then it will always be "private field + public accessors". In Java, people typically called these "properties", or at least that's how I remember. – Recaption

Good answer; minor addition: you can mark a property as @JvmField to have it compile to a field. – Sublunary

Ah yes, that is true. I'm not sure why I forgot to mention that. – Recaption

@Recaption Thank you very much for your comment , adding JvmField annotaion solve problem that cause headache for me – Horoscopy