如何从 Kotlin 中的 Java 枚举中获取名称

Question

I have a project that is written with both Java and Kotlin languages and recently I faced next issue.

Let's say we have MyMonth enum:

public enum MyMonth {
    JAN("January"),
    FEB("February");

    private final String name;

    MyMonth(final String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

Then in Kotlin when we print the name of the month:

fun main() {
    val month = MyMonth.JAN
    println(month.name)
}

we get:

JAN

which is what is described in the documentation https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-enum/name.html , however actually the name should be January .

Is there a way to get a name in Kotlin that is specified in Java enum?

UPD: My Kotlin version is 1.3.30-release-170

UPD2: IDEA even shows me that name is coming from the getName() method defined in Java:

UPD3: When we explicitly use .getName() it works, however it looks kind of weird

Answer 1

Your Java API has name as a private field. Nothing can access it, not in Java nor Kotlin.

If you want to access it, add eg the following to the Java API:

public String getMonthName() { return name; }

...and then access it from Kotlin as

val month = MyMonth.JAN.monthName

Answer 2

You can call the getter directly instead of using the property syntax:

fun main() {
    val name = MyMonth.JAN.getName()
    println(name)
}

Answer 3

You should be calling MyMonth.JAN.name instead.

Remember, with the Java -> Kotlin interop, any getter in Java like the one you have defined

public String getName() {
    return name;
}

Gets the get dropped when you're calling it from Kotlin. so when you do MyMonth.JAN.name you aren't accessing the private variable name which you set in the enum. You are actually accessing the getName() method which you defined

Answer 4

enum is now low usage. You can use IntDef instead of enums.

@IntDef(MyMonth.JAN, MyMonth.FEB)
@Retention(AnnotationRetention.SOURCE)
annotation class MyMonth  {
    companion object {
        const val JAN = 0
        const val FEB = 1

        fun getDisplayString(toDoFilterTypes: Int): String {
            return when (toDoFilterTypes) {
                JAN -> "All"
                FEB -> "Job"
                else -> "N/A"
            }
        }
    }
}