Is there a way to not inherit a specific property? - kotlin

Question

I'm trying to group my classes like images.
It is a structure in which one header and several items are gathered in one group to form a list.
If the Header property and Item list properties are placed in the sealed class, the subclass inherits this, so the structure becomes strange.
So, I want to make it impossible to inherit only Header property and Item list property in sealed class. Is there a way?
GroupedItem
sealed class GroupedItem(val layoutId : Int = 1) {
val header: Header = Header() // I want to make inheritance impossible
val itemList: List<Item> = listOf() // I want to make inheritance impossible
data class Header(
val id: String = "",
) : GroupedItem(someValue)
data class Item(
val id: String = "",
val set: Int = 1,
) : GroupedItem(someValue)
}
Grouping example
for (i in 0 until headerNumber) {
val headerText = "Header $i"
val header = GroupedItem.Header(headerText)
val itemList = arrayListOf<GroupedItem.Item>()
val indexNumber = Random.nextInt(2, 5)
for (j in 0 until indexNumber) {
val itemText = "Item $j"
itemList.add(GroupedItem.Item(itemText))
}
val groupedItem = GroupedItem(header, itemList)
groupedItemList.add(groupedItem)
}
ADDED
Main
fun main() {
val test = RoutineItem.Header()
println(test.id)
}
ERROR
Exception in thread "main" java.lang.StackOverflowError
at RoutineItem$Header.<init>(hello.kt)
at RoutineItem$Header.<init>(hello.kt:18)
at RoutineItem.<init>(hello.kt:15)
at RoutineItem.<init>(hello.kt)
at RoutineItem$Header.<init>(hello.kt:22)
at RoutineItem$Header.<init>(hello.kt:18)
at RoutineItem.<init>(hello.kt:15)
at RoutineItem.<init>(hello.kt)
``

Answer 1

The way you're defining it, a Header is a GroupedItem, and every GroupedItem has a Header, which is incorrect, right? It seems like you want one of these:
GroupedItem represents a category of items that go in your groups, i.e. Headers and ItemLists:
You can use an interface, but a sealed class is fine for this (and gives you the GroupedItem.Thing namespacing). Since GroupedItem is a general category, it shouldn't contain a Header or anything else, just like a Vehicle shouldn't have a Car property
GroupedItem represents a structure that contains a Header and an ItemList (possibly optional):
In this case, Header isn't a GroupedItem at all (same as a Wheel isn't a Car) and shouldn't inherit from it - it has no relation to that class. GroupedItem just happens to include a Header as a property.
If you want the GroupedItem.Thing naming scheme to keep things organised, you can just make Header a class within GroupedItem (not an inner class though):
class GroupedItem(
val header: Header = Header(),
val itemList: List<Item> = listOf()
){
data class Header(
val id: String = "",
)
data class Item(
val id: String = "",
val set: Int = 1,
)
}
you'll have to sort out where layoutId is coming from though.
honestly though, I think you probably want both of these things:
GroupedItem to represent things that go in groups
Group for an actual concrete group of those things
class Group(
val header: Header = Header()
val itemList: List<Item> = listOf()
)
sealed class GroupedItem(val layoutId : Int = 1) {
data class Header(
val id: String = "",
) : GroupedItem(someValue)
data class Item(
val id: String = "",
val set: Int = 1,
) : GroupedItem(someValue)
}