Java allows default values for interface fields, so why does Kotlin not allow it? or at the very least delegation 😦

Kotlin allows default values in interface, but only with using of getters

interface A {
    val x: Int
        get() = 1 // OK
    
    val y: Int = 1 // Error
}

If you write

val y = 1

you assume that

y

have backing field, but interfaces can't have state, so you can declare only custom getters/setters

but can't java have backing fields in interfaces?

when you declare field in java interface that field is static

interface Some {
    int x = 1;
}

...
// prints 1
System.out.println(Some.x)

@Hullaballoonatic You're probably looking for

const val

in the

companion object

of the

interface

.

What is the intellectual value of interfaces having

no

state vs having a

default

state? (edit: yeah, gotcha. they already support default state via static field values) @louiscad I actually am looking for default instance field values, not static ones, but thanks as that further illustrates the distinction

Memory state can only be stored in fields. Interfaces don't support fields. The "interfaces" that do are called abstract classes. A getter with a default implementation can work in an actual interface though, and that value can be cached in the companion object.

yeah, abstract classes are a feature i rarely use, given that kotlin's interfaces have so much teeth already. i end up implementing interfaces via delegation more often.

Abstract classes have use cases too

Yeah I use them occasionally.... When I'm not using sealed classes instead