2022.9.26 Kotlin-枚举类&密封类

2022-09-26

Kotlin-枚举类&密封类

1.枚举类

枚举类,用来定义常量集合的一种特殊类

enum class Direction {
    EAST,
    WEST,
    SOUTH,
    NORTH
}

fun main(){
    println(Direction.EAST)
}

传入一个构造函数

enum class Direction(private val coordinate: Coordinate){
    EAST(Coordinate(1,0)),
    WEST(Coordinate(1,0)),
    SOUTH(Coordinate(1,0)),
    NORTH(Coordinate(1,0));

    fun updateCoordinate(playerCoordinate: Coordinate) = Coordinate(playerCoordinate.x + coordinate.x,playerCoordinate.y + coordinate.y)
}

fun main(){
    println(Direction.EAST.updateCoordinate(Coordinate(10,20)))
}

1.1 代数数据类型

可以用来表示一组子类型的闭集,枚举类就是一种简单的ADT

enum class LicenseStatus {
    UNQUALIFIED,
    LEARNING,
    QUALIFIED
}

class Driver(var status: LicenseStatus){
    fun checkLicense() : String{
        return when(status){
            LicenseStatus.UNQUALIFIED -> "没资格"
            LicenseStatus.LEARNING -> "在学"
            LicenseStatus.QUALIFIED -> "有资格"
        }
    }
}

fun main(){
    println(Driver(LicenseStatus.QUALIFIED).checkLicense())
}

2.密封类

对于更复杂的ADT,可以使用Kotlin的密封类(sealed class)来实现更复杂的定义,密封类可以用来定义一个类似于枚举类的ADT,但你可以更灵活地控制某个子类型

密封类可以有若干个子类,要继承密封类,这些子类必须和它定义在同一个文件里

sealed class LicenseStatus {
    object UnQualified : LicenseStatus()
    object Learning : LicenseStatus()
    //如果是Qualified,就需要指定licenseId
    class Qualified(val licenseId: String) : LicenseStatus()
}

class Driver(var status: LicenseStatus){
    fun checkLicense(): String{
        return when(status){
            is LicenseStatus.UnQualified -> "没资格"
            is LicenseStatus.Learning -> "在学"
            is LicenseStatus.Qualified -> "有资格,驾驶证编号: ${(this.status as LicenseStatus.Qualified).licenseId}"
        }
    }
}

fun main(){
    val status = LicenseStatus.Qualified("114514")
    val driver = Driver(status)
    println(driver.checkLicense())
}