有人能给我解释一下继承在Kotlin中是如何工作的吗？我在Kotlin的继承中挣扎，似乎无法完成我在Java中所知道的简单任务。
在Java中，我们可以这样做：

class Base {...}
class AClass extends Base {...}
class BClass extends Base {...}

字符串
以及一个这样做的服务：

Base myMethod(...) {
    return new AClass() //or new BClass()
}

型
因为AClass是Base，BClass也是Base。
当我在Kotlin中尝试相同的操作时，我得到了一条错误消息，告诉我在尝试返回AClass或BClass对象的地方需要一个Base对象。
类型不匹配。必需：找到的基：AClass？
那么，Kotlin是如何实现这样简单的事情的呢？
编辑：Kotlin类

sealed class GameObject {
    abstract val objectId: String
    abstract val objectName: String
}

sealed class Resource(
    override val objectId: String,
    override val objectName: String,
    open val resourceType : ResourceType
): GameObject() {
    abstract val usageEffects: List<UseEffect>
    abstract val eolEffects: List<DiscardEffect>
    abstract val recipes: List<Recipe>
    abstract val providedEnergy: Int
    abstract val neededEnergy: Int
}

data class BaseResource(
    override val resourceType: ResourceType,
    override val usageEffects: List<UseEffect> = emptyList(),
    override val eolEffects: List<DiscardEffect> = emptyList(),
    override val recipes: List<Recipe> = emptyList(),
    override val providedEnergy: Int = 0,
    override val neededEnergy: Int = 0,
): Resource("RES", "RES", resourceType)

data class ProductionFactor(
    override val resourceType: ResourceType,
    override val usageEffects: List<UseEffect> = emptyList(),
    override val eolEffects: List<DiscardEffect> = emptyList(),
    override val recipes: List<Recipe> = emptyList(),
    val productivity: Int = 1,
    override val providedEnergy: Int = 0,
    override val neededEnergy: Int = 0,
    val combustibleTypes: List<ResourceType> = emptyList()
    var combustibles: List<Resource> = mutableListOf()
): Resource("RES", "RES", resourceType)

型
这些是我与之斗争的一些对象。
现在的用例：所有的'Resource'对象（包括BaseResource和ProductionFactor）都存储在这个map中：

var resourcesMap: EnumMap<ResourceType, out Resource>

型
根据事件的不同，我想返回一个Resource对象的副本，它在这个map中存储为“value”（相对于“key”的ResourceType）：

fun getCard(card: Card): GameObject? {

    var gameObject: GameObject? = null
    val type = card.cardType
    when (type) {
        CardType.TERRITORY -> {
            val territoryCard = card as TerritoryCard
            val territoryType = territoryCard.territory
            gameObject = territoriesMap[territoryType]?.copy(objectId = card.cardId, objectName = card.cardName)
        }
        CardType.RESOURCE -> {
            val resourceCard = card as ResourceCard
            val resourceType = resourceCard.resource
            when (val resource = resourcesMap[resourceType]) {
                is BaseResource -> {
                    gameObject = resource.copy(objectId = card.cardId, objectName = card.cardName)
                }
                is ProductionFactor -> {
                    gameObject = resource.copy(objectId = card.cardId, objectName = card.cardName)
                }

                null -> println("Unknown type")
            }
        }
        CardType.BUILDING -> {
            val buildingCard = card as BuildingCard
            val buildingType = buildingCard.building
            gameObject = buildingsMap[buildingType]?.copy(objectId = card.cardId, objectName = card.cardName)
        }
    }

    return gameObject
}

型