Question

我正在创建一个非常简单的kotlin程序，并且看到父类的行为很奇怪。

代码是：

fun makeSalt(name:String) = Spice(name, "non-spicy")
fun main(args: Array<String>) {
    var salt : Spice = Spice("salt", "non-spicy")

    println("Salt heat = ${salt.heat}")

    val spicelist = listOf<Spice>(
        Spice("salt", "non-spicy"),
        Spice("turmeric", "mild"),
        Spice("Pepper", "hot"),
        Spice("Chilli", "hot"),
        Spice("Sugar", "non-spicy")
    )

    val mildSpices = spicelist.filter{it.heat <=5}

    val salt2 = makeSalt("rock salt")

    val bhoot : SubSpice = SubSpice("bhoot", "hot")
}


open class Spice(open var name:String, open var spiciness:String = "mild" ){
    var heat : Int = 5
        get() = when (spiciness){
            "mild"->5
            "hot"->10
            "non-spicy"->1
            else -> 0

        }

    init{
        if(spiciness === null) {println("spiciness is null")}
        else println("Spiciness of ${name} = ${spiciness}; heat = ${heat}")
    }
}

class SubSpice(override var name:String, override var spiciness:String = "hot") : Spice(name, spiciness){

}

执行此程序时，输出为：

Spiciness of salt = non-spicy; heat = 1
Salt heat = 1
Spiciness of salt = non-spicy; heat = 1
Spiciness of turmeric = mild; heat = 5
Spiciness of Pepper = hot; heat = 10
Spiciness of Chilli = hot; heat = 10
Spiciness of Sugar = non-spicy; heat = 1
Spiciness of rock salt = non-spicy; heat = 1
spiciness is null

如您所见，当我创建子类的对象时，父类的变量spiciness变为null。有人可以解释为什么吗？我希望它为null，因为它也具有默认参数"mild"

Answer 1

在不覆盖任何getter / setter方法时，您正在使用open var。

您要引入奇怪的初始化冲突，因为Spice.init（父类构造函数）在SubSpice.init之前被调用，并且通过覆盖字段，它们不再与父构造函数一起初始化-而是一旦{ {1}}已构建。

从父类的变量和子构造函数的Subspice删除open关键字，这样字段将在override var类中正确初始化，并且其Spice块应成功运行

Answer 2

要在Pawel的答案中添加其他信息：

如果使用open覆盖属性，则基类中的init块将在初始化派生属性之前运行。

查看文档：{{3}}

因此，如果我们像Pawel建议的那样更改代码，最终将得到如下结果：

fun main(args: Array<String>) {
    Spice("salt", "non-spicy")
    Spice(name="spice")
    SubSpice(name = "bhoot", spiciness = "hot")
    SubSpice(name="subspice")
}

open class Spice(var name:String, var spiciness : String = "mild" ) {
    var heat : Int = 5
        get() = when (spiciness){
            "mild"->5
            "hot"->10
            "non-spicy"->1
            else -> 0
        }

    init{
        if(spiciness === null) {println("spiciness is null")}
        else println("Spiciness of ${name} = ${spiciness}; heat = ${heat}")
    }
}

class SubSpice(name: String, spiciness : String = "hot") : Spice(name, spiciness) {
}

哪个输出：

Spiciness of salt = non-spicy; heat = 1
Spiciness of spice = mild; heat = 5
Spiciness of bhoot = hot; heat = 10
Spiciness of subspice = hot; heat = 10

父类的init块中的null值

2 个答案: