技術標籤：kotlin基礎

Kotlin 中的Class

文章目錄

• • • Kotlin 中的Class
    • • 特點
      • • abstract class
        • Subclass（子類）
        • • 正確繼承
          • 錯誤示範
          • 注意
        • Sample（例子）
        • • Run and output（執行和輸出）
        • 關鍵字
        • • with
        • 多個引數的構造
        • • Sample
          • Run and output（執行和輸出）

特點

預設情況下，在Kotlin中，類是final類，不能子類化(被繼承)，只允許繼承abstract class 或者被關鍵字open標記的class

abstract class

abstract class Dwelling(private var
 
 residents:Int) {
    abstract val buildMaterial:String
    abstract val capacity:Int
    fun hasRoom():Boolean{
        return residents < capacity
    }

}

Subclass（子類）

 class RoundHut(residents: Int) : Dwelling(residents) {
    override val buildMaterial: String = "Stone"
    override
 
 val capacity: Int = 4
}

正確繼承

open class RoundHut(residents: Int) : Dwelling(residents) {
    override val buildMaterial: String = "Stone"
    override val capacity: Int = 4
}
class RoundTower(residents: Int) : RoundHut(residents) {
    override val buildMaterial: String = "Stone"
 

    override val capacity: Int = 4
}

錯誤示範

This type is final, so it cannot be inherited from RoundHut

 class RoundHut(residents: Int) : Dwelling(residents) {
    override val buildMaterial: String = "Stone"
    override val capacity: Int = 4
}
class RoundTower(residents: Int) : RoundHut(residents) {
    override val buildMaterial: String = "Stone"
    override val capacity: Int = 4
}

注意

定義抽象類時不需要使用open關鍵字, 因為當前表示abstract的,可以子類化的,修飾語open是多餘的

Sample（例子）

 fun main(){
        val roundTower = RoundTower(4)
        with(roundTower){
            println("\nRound Tower\n ====")
            println("Material:${buildMaterial}")
            println("Material:${capacity}")
            println("Has room?${hasRoom()}")
        }
 
 }

Run and output（執行和輸出）

Round Tower
 ====
Material:Stone
Material:4
Has room?false

關鍵字

with

定義：以給定的[receiver]作為其接收方，呼叫指定的函式[block]並返回其結果

with後跟()中的例項名，後跟包含要執行的操作的{}

 with(roundTower){
            println("\nRound Tower\n ====")
            println("Material:${buildMaterial}")
            println("Material:${capacity}")
            println("Has room?${hasRoom()}")
        }

這裡[receiver] 是roundTower, {}裡為函式塊

多個引數的構造

class RoundTower(
    residents: Int,
    val floors: Int = 2) : RoundHut(residents) {
    override val buildMaterial: String = "Stone"
    override val capacity: Int = 4 * floors
}

其中建構函式中宣告 val floors: Int = 2 ,表示將floors賦值為2（預設值）,當沒有將floors的值傳遞給建構函式時，可以使用預設值建立物件例項

Sample

val roundTower = RoundTower(4)
with(roundTower){
    println("\nRound Tower\n ====")
    println("Material:${buildMaterial}")
    println("Material:${capacity}")
    println("Has room?${hasRoom()}")
}

Run and output（執行和輸出）

Round Tower
  ====
Material:Stone
Material:8
Has room?true