在 Kotlin 中，如何转换 Int到一个 Int

发布于12月29日

我在Kotlin中使用的是HashMap<Int, Int>，当I为get时，返回类型为Int?.

How can I convert the Int? to an Int?

So far I've tried using Int?.toInt(), but that seems to be returning an Int?.

I'm writing a Fibonacci function, and my code looks like:

val fibMemo : Map<Int, Int> = HashMap<Int,Int>()
fun fibN(n:Int) : Int {
    if (n == 0 || n == 1) return 1
    if (fibMemo.containsKey(n))
        // Error here: Type mismatch: inferred type is Int? but Int was expected
        return fibMemo.get(n)?.toInt()
    else {
        val newNum : Int = fibN(n-1) + fibN(n-2)
        fibMemo.put(n, newNum)
        return newNum
    }
}

推荐答案

The direct answer, use the !! operator to assert that you trust a value is NOT null and therefore changing its type to the non null equivalent. A simple sample showing the assertion allowing the conversion (which applies to any nullable type, not just Int?)

val nullableInt: Int? = 1
val nonNullableInt: Int = nullableInt!! // asserting and smart cast

转换值的另一种方法是通过空判断.在上面的代码中不有用，但在其他代码中有用(参见Checking for null in conditions):

val nullableInt: Int? = 1
if (nullableInt != null) {
   // allowed if nullableInt could not have changed since the null check
   val nonNullableInt: Int = nullableInt
}

这个问题也可以通过习惯性地处理可空性问题来回答:In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them