柯特林猫王符(？:)
猫王符(？:)用于返回非空值，即使条件表达式为空。它也用于检查值的空值安全性。
在某些情况下，我们可以声明一个可以保存空引用的变量。如果一个变量 st 包含空引用，在程序中使用 st 之前，我们将检查它的可空性。如果变量 st 被发现不为 null，那么它的属性将使用其他非 null 值。
// Kotlin Program without using Elvis Operator
fun main(args: Array<String>)
{
var st: String? = null
var st1: String? = "Geeks for Geeks"
var len1: Int = if (st != null) st.length else -1
var len2: Int = if (st1 != null) st1.length else -1
println("Length of st is ${len1}")
println("Length of st1 is ${len2}")
}
输出:
Length of st is -1
Length of st1 is 15
// Kotlin Program using Elvis Operator
fun main(args: Array<String>)
{
var st: String? = null
var st1: String? = "Geeks for Geeks"
var len1: Int = st ?.length ?: -1
var len2: Int = st1 ?.length ?: -1
println("Length of st is ${len1}")
println("Length of st1 is ${len2}")
}
输出:
Length of st is -1
Length of st1 is 15
