kotlin半生對象

伴侶對象 (Companion object)

• If you need a function or a property to be tied to a class rather than to instances of it (similar to static in java), you can declare it inside a companion object:

  如果需要將函數或屬性綁定到類而不是實例(類似于java中的static)，則可以在同伴對象中聲明它：

• You can omit the name, in which case the name defaults to Companion,

  您可以省略名稱，在這種情況下，名稱默認為Companion，

  companion object <Optional Name>{//Companion Object Body }

• Companion objects members can only be accessed via the containing class name, not via instances of the class.

  伴侶對象成員只能通過包含的類名稱訪問，而不能通過類的實例訪問。

• A class has only one companion object.

  一個類只有一個伴隨對象。

• Companion object initializes when class is loaded, (typically when first time reference from other code).

  伴侶對象在加載類時初始化(通常是在第一次從其他代碼引用時)。

• Companion object has its own init block.

  伴隨對象具有其自己的init塊。

• The companion object is a singleton.

  伴隨對象是單例。

Kotlin中的伴隨對象特征程序 (Program for companion object features in Kotlin)

package com.includehelp//Declare class class Car{//class init blockinit {println("Init Block of Class")}//Make companion objectcompanion object {//companion object init blockinit {println("Init Block of Companion object")}//property of companion objectval name="Tata Altroz !! "//function in companion objectfun printName(){println("Your Car name : $name")}} }//Main Function, Entry Point of Program fun main(){//Call method with Class name, //without create Instance of class, //like static method in javaCar.printName()//access Property using class nameval nameLen = Car.name.lengthprintln("Car Name Length : $nameLen") }

Output:

輸出：

Init Block of Companion object Your Car name : Tata Altroz !! Car Name Length : 15

翻譯自: https://www.includehelp.com/kotlin/companion-object-features.aspx

kotlin半生對象

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