kotlin半生对象

伴侣对象 (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:

  如果需要将函数或属性绑定到类而不是实例(类似于java中的static)，则可以在同伴对象中声明它：

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

  您可以省略名称，在这种情况下，名称默认为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.

  伴侣对象成员只能通过包含的类名称访问，而不能通过类的实例访问。

• A class has only one companion object.

  一个类只有一个伴随对象。

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

  伴侣对象在加载类时初始化(通常是在第一次从其他代码引用时)。

• Companion object has its own init block.

  伴随对象具有其自己的init块。

• The companion object is a singleton.

  伴随对象是单例。

Kotlin中的伴随对象特征程序 (Program for companion object features in Kotlin)

package com.includehelp
//Declare class
class Car{
//class init block
init {
println("Init Block of Class")
}
//Make companion object
companion object {
//companion object init block
init {
println("Init Block of Companion object")
}
//property of companion object
val name="Tata Altroz !! "
//function in companion object
fun 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 java
Car.printName()
//access Property using class name
val nameLen = Car.name.length
println("Car Name Length : $nameLen")
}

Output:

输出：

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

翻译自: https://www.includehelp.com/kotlin/companion-object-features.aspx

kotlin半生对象