fun main(args: Array<String>) {
// val parent: Parent = Child()
val parent: Parent = Parent()
// val child: Child? = parent as Child //进行类型转换，如不成功则抛出异常
val child: Child? = parent as? Child //进行类型转换，如不成功返回null
println(child)
if (parent is Child) {
println(parent.name)
}
val string: String? = "Hello"
if (string is String) { //智能转换1
println(string.length)
}
if (string != null) { //智能转换2
println(string.length)
}
println(string!!.length) //告诉编译器当前已确定字符串不为空
}
运行结果
